I've explained this before, such as over chat or talks with slides,
so it's time to have a proper version in our docs.
It doesn't really belong in the README, because a user shouldn't have to
understand these internal details.
The way Go builds with -toolexec spawn sub-processes is a bit tricky,
so I've attempted to demonstrate it with a vertical tree using Unicode.
Each added indentation level is one more sub-process level.
See https://github.com/burrowers/garble/issues/121#issuecomment-695935859.
In some rare cases, it's nearly impossible to write a test for a change,
but they are truly so rare that we shouldn't give any ideas here.
By default, all contributors should try to write a test for every
change that changes what the code is meant to do.
Many files were missing copyright, so also add a short script to add the
missing lines with the current year, and run it.
The AUTHORS file is also self-explanatory. Contributors can add
themselves there, or we can simply update it from time to time via
git-shortlog.
Since we have two scripts now, set up a directory for them.
