📚 Add serialization docs for gradient stops and path data

render-wasm/docs/serialization.md

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+# Serialization
+
+## Paths
+
+Paths are made of segments of **28 bytes** each. The layout (assuming positions in a `Uint8Array`) is the following:
+
+| Offset | Length (bytes) | Data Type | Field   |
+| ------ | -------------- | --------- | ------- |
+| 0      | 2              | `u16`     | Command |
+| 2      | 2              | `u16`     | Flags   |
+| 4      | 4              | `f32`     | `c1_x`  |
+| 8      | 4              | `f32`     | `c1_y`  |
+| 12     | 4              | `f32`     | `c2_x`  |
+| 16     | 4              | `f32`     | `c2_y`  |
+| 20     | 4              | `f32`     | `x`     |
+| 24     | 4              | `f32`     | `y`     |
+
+**Command** can be one of these values:
+
+- `:move-to`: `1`
+- `:line-to`: `2`
+- `:curve-to`: `3`
+- `:close-path`: `4`
+
+**Flags** is not being used at the moment.
+
+## Gradient stops
+
+Gradient stops are serialized in a `Uint8Array`, each stop taking **5 bytes**.
+
+| Offset | Length (bytes) | Data Type | Field       |
+| ------ | -------------- | --------- | ----------- |
+| 0      | 1              | `u8`      | Red         |
+| 1      | 1              | `u8`      | Green       |
+| 2      | 1              | `u8`      | Blue        |
+| 3      | 1              | `u8`      | Alpha       |
+| 4      | 1              | `u8`      | Stop Offset |
+
+**Red**, **Green**, **Blue** and **Alpha** are the RGBA components of the stop.
+
+**Stop offset** is the offset, being integer values ranging from `0` to `100` (both inclusive).