docs(contributing): explain project scope explicitly (#765)

CONTRIBUTING.md

@@ -7,13 +7,23 @@
 
 > Tip: This repo supports `corepack`. Just enable it `corepack enable` and this repo will warn you if you try to use another package manager.
 
+## Scope
+
+The `@coveo/platform-client` is an open source project. Therefore by nature its scope is limited to Coveo's endpoints that are **public**, **documented**, and **stable**. Any change to an endpoint that doesn't comply to all of the criteria enumerated above will likely be rejected / heavily challenged by the maintainers of the project at the pull request stage.
+
+-   _public_: available in production.
+-   _documented_: available on [Swagger](https://platform.cloud.coveo.com/docs).
+-   _stable_: the change is not deemed to be temporary, or part of a rapid iteration process.
+
+In case your changes don't fall within the scope **yet**, but you still want to be able to use them, we recommend [extending the client](https://github.com/coveo/platform-client#extending-the-client) in your own project.
+
 ## Guidelines
 
 -   Make sure your changes are fully tested (when applicable).
 -   We tend to avoid comments in our code base, we strongly prefer good naming and code structure.
 -   Avoid pushing similar changes in different commits if it's within the same feature, because we want the changelogs to be clear and simple. To avoid that, there are at least 2 options:
     1. Squash the commits into one when merging (you need to edit the final commit message though)
-    1. amend the previous commit when making related changes (`git commit --amend --no-edit`)
+    2. amend the previous commit when making related changes (`git commit --amend --no-edit`)
 
 ## Commit messages