syncthing/etc/linux-desktop/README.md

Desktop Entries

This directory contains files to integrate Syncthing in your desktop environment (DE). Specifically this works for DEs that implement the XDG Desktop Menu Specification, which is virtually every DE.
To add Syncthing to desktop menus for all users, copy the .desktop files to /usr/local/share/applications (root required). To add it for just your user, copy them to ~/.local/share/applications.
To start Syncthing automatically, you have two options: Either you go to the autostart settings of your DE and choose Syncthing or you copy the syncthing-start.desktop file to ~/.config/autostart.
For more information refer to the ArchWiki page on Desktop entries