Add support for .tar.gz linux target to include the .desktop file

[t3chguy]

Given the .desktop file is responsible for https://www.electron.build/linux.html#protocols support - maybe would want to also include an INSTALL file with basic instructions on where to copy the .desktop file to make it work.

Otherwise https://www.electron.build/app-builder-lib.interface.platformspecificbuildoptions#protocols should be updated with the caveats of which platform packages it does not support.

[mmaietta]

Very fair point.

Curious on your thoughts here for the INSTALL file. If electron-builder were to create it, it wouldn't be able to be localized text. Not sure if that'd be a blocker for auto-including one

What would you like included with the INSTALL file? (Off the top of my head, I'm not familiar with how/where .desktop files need to be copied to and/or if system commands are needed to run in order to register it)

[t3chguy]

I think leaving the INSTALL file to the application to insert at least for now is a sane approach, the alternative for getting the .desktop file would be to build .deb then extract the .desktop file and then build the .tar.gz which is pretty crap :D