add community Snap template

Co-Authored-By: N林博仁(Buo-ren Lin) <lin-buo-ren@users.noreply.github.com>
Co-Authored-By: NMarius Gripsgard <marius@ubports.com>

community/Linux/Snap.gitignore

+# gitginore template for creating Snap packages
+# website: https://snapcraft.io/
+
+parts/
+prime/
+stage/
+*.snap
+
+# Snapcraft global state tracking data(automatically generated)
+# https://forum.snapcraft.io/t/location-to-save-global-state/768
+/snap/.snapcraft/
+
+# Source archive packed by `snapcraft cleanbuild` before pushing to the LXD container
+/*_source.tar.bz2