Isn’t the commit message a better place to add what and why? You might need to feed some info that the agent doesn’t have access to “we are developing feature X this change will such and such to blah blah”. The agent will write a pretty good commit message most of the times. Why do you need a markdown file? Are releasing new versions of the software for third parties?

Cheaper and faster retrieval to be added to the context and discoverable by the agent.

You need more git commands to find the right commit that contains the context you want (either you the human or the LLM burning too many token and time) than just include the right MD file or use grep with proper keywords.

Moreover you could need multiple commits to get the full context, while if you ask the LLM to keep the MD file up to date, you have everything together.