🚀 Include completions in .deb packages

The .deb packages don't seem to include the bash and zsh completions:

```
$ dpkg -c git-delta_0.11.3_amd64.deb
drwx------ root/root 0 2021-12-16 11:00 ./
drwxr-xr-x root/root 0 2021-12-16 11:00 ./usr/
drwxr-xr-x root/root 0 2021-12-16 11:00 ./usr/bin/
-rwxr-xr-x root/root 5518912 2021-12-16 11:00 ./usr/bin/delta
drwxr-xr-x root/root 0 2021-12-16 11:00 ./usr/share/
drwxr-xr-x root/root 0 2021-12-16 11:00 ./usr/share/doc/
drwxr-xr-x root/root 0 2021-12-16 11:00 ./usr/share/doc/git-delta/
-rw-r--r-- root/root 69847 2021-12-16 11:00 ./usr/share/doc/git-delta/README.md
-rw-r--r-- root/root 1283 2021-12-16 11:00 ./usr/share/doc/git-delta/copyright
```

Would it be possible to include them?

Start by inspecting the package contents with `dpkg -c` and locating the existing bash and zsh completion definitions alongside the .deb packaging entry point. Done means rebuilding the package shows both completion files installed in the expected system locations, while the delta binary and documentation remain included.

Written by the indexing model from the issue text.