linux/README.md - add missing dependencies

[bradloh]

I tried installing the Linux app on a recent install of Ubuntu and ran into a few missing dependencies. I looked up the equivalent packages in Arch and Fedora and tested the new install commands in containers (archlinux:latest and fedora:latest).

[AhmetTumis]

Yeah pulse audio was missing on my side as well, cmake is a duh though.

[bradloh]

cmake is a duh though.

For developers and advanced users, yes. But:

• I think it's good form to have copy/paste install instructions work on clean installs of supported platforms.
• Given that I couldn't easily find a package for this application, I suspect more casual users may try to install this.

[kavishdevar]

thanks!

btw, do give #241 a try. download a build from Actions.

[bradloh]

Thanks @kavishdevar ! I downloaded the appimage yesterday and gave it a quick try, but then reverted back to this one. When I get a bit more free time I'll try to leave some feedback on your PR.