README instructions for writing blog entries do not work as-is #94

The README currently says:

You can pull the repo, run make dev, and edit the page via Keystatic with the nice UI

I did so, and noticed that this had an implicit dependency on Bun. This dependency should be called out.

After installing Bun, I got a different failure due to the astro not being installed:

❯ make dev        
bun run dev
$ astro dev
/bin/bash: astro: command not found
error: script "dev" exited with code 127
make: *** [dev] Error 127

This is because, the user needs to do a make install before make dev.

I did end up writing it in Markdown, since I'm familiar with that.