Add desktop entry file for Linux app launchers

Refs <https://specifications.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html>

PR #3351 <https://github.com/Genymobile/scrcpy/pull/3351>
Replaces PR #296 <https://github.com/Genymobile/scrcpy/pull/296>
Fixes #295 <https://github.com/Genymobile/scrcpy/issues/295>
Fixes #748 <https://github.com/Genymobile/scrcpy/issues/748>
Fixes #1636 <https://github.com/Genymobile/scrcpy/issues/1636>

Co-authored-by: Chih-Hsuan Yen <yan12125@gmail.com>
Signed-off-by: Romain Vimont <rom@rom1v.com>