chore: explicitly lists out which definitions come from another RFC

Signed-off-by: Vincent Biret <[email protected]>

Author: baywet

src/oas.md

@@ -60,7 +60,7 @@ sub-delims          = "!" / "$" / "&" / "'" / "(" / ")"
                     / "*" / "+" / "," / ";" / "="
 ```
 
-Here, all characters definitions are taken from [RFC 3986](https://tools.ietf.org/html/rfc3986). The `path-template` is directly derived from [RFC 3986, section 3.3](https://datatracker.ietf.org/doc/html/rfc3986#section-3.3).
+Here, `pchar`, `unreserved`, `pct-encoded` and `sub-delims` definitions are taken from [RFC 3986](https://tools.ietf.org/html/rfc3986). The `path-template` is directly derived from [RFC 3986, section 3.3](https://datatracker.ietf.org/doc/html/rfc3986#section-3.3).
 
 ### Media Types