Add bash-completion package

[casperklein]

Description

bash-completion package added.

Motivation and Context

Bash completion did not work for the pihole command.

How Has This Been Tested?

Yes. After installing the bash-completion package, bash completion works for the pihole command.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.