Mach's bash completion now completes arguments and subcommands

[Andrew Halberstadt]

Hi everyone,

Just a quick note that the bash completion
<https://searchfox.org/mozilla-central/source/python/mach/bash-completion.sh>
script that ships with
mach now completes subcommands and arguments. Previously
it would only complete the main set of commands. This should
help with discoverability and ease of use.

If you were unaware of this script's existence, you can find
installation instructions
<https://firefox-source-docs.mozilla.org/python/mach/usage.html#auto-completion>
in the docs. If using the shell that ships
with mozilla-build, be sure to source the script in ~/.bash_profile
(might need to be created). Bug 1519854
<https://bugzilla.mozilla.org/show_bug.cgi?id=1519854> tracks getting this
script
installed via |mach bootstrap|.

Only bash and zsh are supported at this time. Bug 1519858
<https://bugzilla.mozilla.org/show_bug.cgi?id=1519858> tracks
adding scripts for more shells (like fish).

Let me know if you have any questions and feel free to chime in
on either of the aforementioned bugs.

Cheers,
Andrew