Ignore Everything But The src Directory With Cargo Watch

I'm working on the rebuild of my site. My test output is going into a `site`` directory next to the `src`` directory. This causes an issue with `cargo watch`` where it gets stuck in a loop every time I build the site. (It sees a change in the directory then reruns the process.)

Passing `--ignore`` flags to `cargo watch`` is one solution. It would be tedious. Instead, I put a `.ignore` file in the root of the project with this in it:

That ignores everything with the `*``, but allows the `src`` directory via the `!src`` line. Combined that lets me edit anything outside the `src`` directory without triggering `cargo watch``.