Add 'contributing' instructions for non-Debian linux

[demfabris]

It's not clear how to build the linux desktop app from source.
Lacking documentation for non debian based distros

[LVMBDV]

I skimmed over CONTRIBUTING.md and did not see anything distro-specific. No mention of apt or anything. What are you talking about?

[demfabris]

I don't think the maintainer understood this issue quite right.
I was using Gentoo Linux and couldn't find any docs regarding installing it from source.

After the huge popularity boom it endup appearing into gentoo repos but i'm still clueless on compiling this app from source

[Nineluj]

@fabricio7p are you referring to the fact that running yarn build-release produces a .deb file that can't be installed on Gentoo (or other non Debian derivatives)?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.