Wrote JNISinglton docs
Wrote JNISinglton docs

I added a few descriptions and links to the empty JNISingleton class doc.

(cherry picked from commit 4eff57d39bb608afdaae8b29f9226481a1520c0b)

ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot