This directory is specified by the XDG Base Directory specification
(https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html).
Quoting:
> User-specific executable files may be stored in $HOME/.local/bin.
> Distributions should ensure this directory shows up in the UNIX $PATH environment variable, at an appropriate place.
So let's actually do this. This way also binaries installed by e.g. Pip
or Cargo will be usable out-of-the-box rather than that the user has to
figure out why it's not appearing in their PATH.
