This ensures that git is added as a run-time dependency of tig and
allows tig to find the git command even if git is not installed in the
user environment. Fixes#5741.
Since version 2.0, tig can use readline for history/completion support,
so add readline as a build input.
Increases closure size from 53 MiB to 54 MiB.
Copy the bash completion script that comes with tig to
$out/etc/bash_completion.d/.
Note: to enable bash completion in NixOS, set
environment.enableBashCompletion = true;
