feat: add local_build.sh script and instructions for local/dev use

[rvagg]

About time this got done, mainly useful for people contributing new recipes, so they can actually test them locally (and we can too).

[richardlau]

I recommend building and running the container(s) with the same uid and gid as the host user otherwise you can end up with mismatched owner/permissions in the mounted volumes after the build(s) completes.

[matthewkeil]

The update works great but the variable needs to be passed to the other two docker commands. I was able to successfully local_build my branch after making the changes below

[matthewkeil]

LGTM!! 🚀