🎉 Add contributing guide.

CONTRIBUTING.md

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+# Contributing Guide #
+
+Thank you for your interest in contributing.. This is a generic guide
+that details how to contribute to this repository in a way that is
+efficient for everyone.
+
+
+## Reporting Bugs ##
+
+We are using [GitHub
+Issues](https://github.com/penpot/penpot-files/issues) for our
+bugs. Before filing a new task, try to make sure your problem doesn't
+already exist.
+
+If you found a bug, please report it, as far as possible with:
+
+- a detailed explanation of steps to reproduce the error
+- a browser and the browser version used
+
+
+## License ##
+
+We are using the CC BY 4.0 (included in the repostory). This is the
+default license that applies to all `.penpot` files that does not have
+explicit license. This license applies to the `.penpot` file itself
+and the original content (made by penpot).
+
+Some penpot files has third-party content (assets, images, etc.)
+licensed with other OpenSource licenses; in this case the content
+license applies (only to assets that already have their own license).
+
+And some penpot files are just containers for third-party content
+(assets, icons, etc.); in this case, the third-party licence will
+apply (and accordingly will be mentioned in the .LICENSE file).
+
+
+## Collaborate ##
+
+If you want to **contribute** with your own **libraries and designs**
+you can do it in two ways:
+
+- 🤟 Create a pull request in this repository by uploading your penpot file.
+- 📧 Send us your penpot file to *info@penpot.app*
+
+The Penpot team will review all libraries and template
+contributions. The approved files will be available in this repository
+for other users to free use. The penpot team is not responsible for
+maintaining third-party libraries and reserves the right to remove
+them from the repository in case the author does not respond to
+possible bugs in it.
+
+The contributed files should be licensed with an recogniced OpenSource
+license. If the license is different that the official one, you should
+contribute the license file in this way:
+
+- `<name-of-the-library>.penpot`
+- `<name-of-the-library>.LICENSE`
+
+Before contributing anything, firstly you should carefully read the
+**DCO** section and format your commits/email accordingly.
+
+
+## Code of conduct ##
+
+As contributors and maintainers of this project, we pledge to respect
+all people who contribute through reporting issues, posting feature
+requests, updating documentation, submitting pull requests or patches,
+and other activities.
+
+We are committed to making participation in this project a
+harassment-free experience for everyone, regardless of level of
+experience, gender, gender identity and expression, sexual
+orientation, disability, personal appearance, body size, race,
+ethnicity, age, or religion.
+
+Examples of unacceptable behavior by participants include the use of
+sexual language or imagery, derogatory comments or personal attacks,
+trolling, public or private harassment, insults, or other
+unprofessional conduct.
+
+Project maintainers have the right and responsibility to remove, edit,
+or reject comments, commits, code, wiki edits, issues, and other
+contributions that are not aligned to this Code of Conduct. Project
+maintainers who do not follow the Code of Conduct may be removed from
+the project team.
+
+This code of conduct applies both within project spaces and in public
+spaces when an individual is representing the project or its
+community.
+
+Instances of abusive, harassing, or otherwise unacceptable behavior
+may be reported by opening an issue or contacting one or more of the
+project maintainers.
+
+This Code of Conduct is adapted from the Contributor Covenant, version
+1.1.0, available from http://contributor-covenant.org/version/1/1/0/
+
+## Developer's Certificate of Origin (DCO) ##
+
+By submitting code you are agree and can certify the below:
+
+    Developer's Certificate of Origin 1.1
+
+    By making a contribution to this project, I certify that:
+
+    (a) The contribution was created in whole or in part by me and I
+        have the right to submit it under the open source license
+        indicated in the file; or
+
+    (b) The contribution is based upon previous work that, to the best
+        of my knowledge, is covered under an appropriate open source
+        license and I have the right under that license to submit that
+        work with modifications, whether created in whole or in part
+        by me, under the same open source license (unless I am
+        permitted to submit under a different license), as indicated
+        in the file; or
+
+    (c) The contribution was provided directly to me by some other
+        person who certified (a), (b) or (c) and I have not modified
+        it.
+
+    (d) I understand and agree that this project and the contribution
+        are public and that a record of the contribution (including all
+        personal information I submit with it, including my sign-off) is
+        maintained indefinitely and may be redistributed consistent with
+        this project or the open source license(s) involved.
+
+Then, all your code patches (**documentation are excluded**) should
+contain a sign-off at the end of the patch/commit description body. It
+can be automatically added on adding `-s` parameter to `git commit`.
+
+This is an example of the aspect of the line:
+
+	Signed-off-by: Andrey Antukh <niwi@niwi.nz>
+
+Please, use your real name (sorry, no pseudonyms or anonymous
+contributions are allowed).

Cocomaterial.LICENSE

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+This penpot file contains assets licences by cocomaterial license:
+https://cocomaterial.com/license

Material-Design-Kit.LICENSE

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+Contains licensed by the material-design license:
+https://github.com/google/material-design-icons/blob/master/LICENSE

README.md

@@ -30,15 +30,8 @@ Once imported you can convert them into shared libraries and use those files in
 
 ## Collaborate ##
 
-If you want to **contribute** with your own **libraries and designs** you can do it in two ways. 
+Look at [CONTRIBUTING](./CONTRIBUTING.md)
 
-- 🤟 Create a pull request in this repository by uploading your penpot file
-
-- 📧 Send us your penpot file to *info@penpot.app*
-
-The Penpot team will review all libraries and template contributions. The approved files will be available in this repository for other users to free use.
-
-**Your contributions are more than welcome!**
 
 ## Terms and conditions ##