Minor edits to CONTRIBUTING.md (#750)

* Clarify PR flow for mongodb employees

Author: hschawe

CONTRIBUTING.md

@@ -60,8 +60,7 @@ To contribute to the project, you should follow the standard GitHub workflow:
    - If there's a Jira ticket for your changes, name the branch after the ticket (e.g. `DOCSP-1234`).
    - If there's no Jira ticket, name the branch after the changes you're making (e.g. `fix_typos`).
 3. Make your changes. Commit them to your branch and push to your fork.
-4. Create a pull request to merge the changes from `<your fork/branch>` into
-   the `mongodb:chatbot/main` branch.
+4. First, push your branch to the upstream repository. Then, create your pull request to merge the upstream branch (i.e., merge `mongodb:chatbot/<your-branch>` into `mongodb:chatbot/main`). Our CI process only runs on branches in the mongodb/chatbot repository, not branches in forks.
 
 ## Network Access