Install manual pages

[lukego]

It would be very handy to have standard Linux man pages installed on lab servers for everybody.

Currently they don't seem to be available:

[luke@lugano-1:~/git/snabbswitch/src]$ apropos fork
fork: nothing appropriate
[luke@lugano-1:~/git/snabbswitch/src]$ man 2 fork
No entry for fork in section 2 of the manual

[domenkozar]

man fork works, so I'll have to check if we're missing just some manpages output.

[domenkozar]

I'll fix man 2 fork, but for apropos we'll need to create and update the database using manpages. See NixOS/nixpkgs#14472