add symlinks in /usr/bin

[anarcat]

Using the stock python:slim container is really difficult if you already have an existing script with #!/usr/bin/python3 on top. You will get a confusing error like:

/usr/bin/bash: line 140: ./check.py: cannot execute: required file not found

... while the script otherwise works perfectly well. I understand that it's relatively standard to install things in /usr/local and I generally support this, but in this very specific case, it seems extremely backwards.

I also understand that, normally, you should install a script with an entrypoint and so on, but we shouldn't let perfection be the enemy of good here.