doc: Update readme to request links to the spec for PRs

README.md

@@ -7,6 +7,10 @@ Supports Language Server Protocol (LSP) version 3.16.0.
 Proposed 3.17 features can be activated using the `proposed` feature flag.
 - **NOTE** that these are unstable and may change between releases.
 
+## Contributing
+
+If you are making a change which adds, removes or modifies the LSP API it is highly appreciated if you link to the spec where this change is described. This gives context to whether the change should be an experimental addition and lets the reviewer double check the changes easily against the spec.
+
 ## Links
 
 [Stable Protocol reference](https://github.com/microsoft/language-server-protocol/tree/gh-pages/_specifications/lsp/3.17/specification.md)