Add xclip or xsel as optional dependency on linux distrobutions

[lil5]

Is your feature request related to a problem? Please describe.
I'm always frustrated when I install gitui and can't copy anything because a dependency is not met

Describe the solution you'd like
To add xclip or xsel as (optional)? dependency to fedora's dnf and other Linux repositories, where needed.

Describe alternatives you've considered
An error message when copying does not succeed prompting the user to install the necessary dependency

[lil5]

#352

[stale]

This issue has been automatically marked as stale because it has not had any activity half a year. It will be closed in 14 days if no further activity occurs. Thank you for your contributions.

[lil5]

Bad bot

[extrawurst]

I do not maintain linux distro packages so this is the wrong place for this request. support for xsel was added via: #390