feat: add chatmode and collection in contributing guide (#290)

* feat: add chatmode and collection in contributing guide

* Update CONTRIBUTING.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: steve-magne

CONTRIBUTING.md

@@ -152,7 +152,7 @@ display:
 
 1. **Fork this repository**
 2. **Create a new branch** for your contribution
-3. **Add your instruction or prompt file** following the guidelines above
+3. **Add your instruction, prompt file, chatmode, or collection** following the guidelines above
 4. **Run the update script** (optional): `node update-readme.js` to update the README with your new file
    - A GitHub Actions workflow will verify that this step was performed correctly
    - If the README.md would be modified by running the script, the PR check will fail with a comment showing the required changes