Add md files for coding agents

[tonisevener]

Phabricator: N/A

Notes

Adding these instructions for coding agents to reference. They outline our preferred architecture with WMFData and WMFComponents, and explain some of the workarounds we have to use to work with older areas of the app.

I've had the most luck using this with Visual Studio code, but you can also try to install the Xcode GitHub Copilot extension for Xcode 16 (Sequoia is still my main setup). More options may become available with Tahoe.

Test Steps

1. To play around with it, install Xcode GitHub Copilot, ensure you are logged into GitHub account in the extension Settings. Turn on agent mode in the extension and ask it to perform work for you. It should make changes that lean on our new patterns, with data controllers in WMFData and components in WMFComponents. It also may ask you to run terminal commands to build and check for compile errors.
2. Do not commit changes.