docs: Improve template documentation slightly; use const, not literal

modules/caddyhttp/reverseproxy/fastcgi/caddyfile.go

@@ -17,6 +17,7 @@ package fastcgi
 import (
 	"encoding/json"
 	"net/http"
+	"strconv"
 
 	"github.com/caddyserver/caddy/v2"
 	"github.com/caddyserver/caddy/v2/caddyconfig"
@@ -136,7 +137,7 @@ func parsePHPFastCGI(h httpcaddyfile.Helper) ([]httpcaddyfile.ConfigValue, error
 		}),
 	}
 	redirHandler := caddyhttp.StaticResponse{
-		StatusCode: caddyhttp.WeakString("308"),
+		StatusCode: caddyhttp.WeakString(strconv.Itoa(http.StatusPermanentRedirect)),
 		Headers:    http.Header{"Location": []string{"{http.request.uri.path}/"}},
 	}
 	redirRoute := caddyhttp.Route{

modules/caddyhttp/templates/templates.go

@@ -113,6 +113,19 @@ func init() {
 // {{.RemoteIP}}
 // ```
 //
+// ##### `.Req`
+//
+// Accesses the current HTTP request, which has various fields, including:
+//
+//    - `.Method` - the method
+//    - `.URL` - the URL, which in turn has component fields (Scheme, Host, Path, etc.)
+//    - `.Header` - the header fields
+//    - `.Host` - the Host or :authority header of the request
+//
+// ```
+// {{.Req.Header.Get "User-Agent"}}
+// ```
+//
 // ##### `.RespHeader.Add`
 //
 // Adds a header field to the HTTP response.