look at local files first

[hamelsmu]

Problem: When you build the context right now, it pulls from the URL. However, what if the URL correpsonds to the current nbdev repo? We should be smart enough to pull from the local generated docs rather than the URL so we don't have to run things twice!

If we want to automate the llms-ctx*.txt creation when we build the docs, I think we need a way to do this?

How to test:

1. Install this branch
2. Go to a nbdev repo, make a local change to a notebook.
3. Run nbdev_docs
4. Run llms_txt2ctx tool, you will see your local changes being reflected appropriately