Clarify docs for Thread.start() godotengine#36032
Clarify docs for Thread.start() godotengine#36032

* Updated docs for Thread.start() to specify that the method argument
must accept one parameter.

(cherry picked from commit d09644dff3ed3552f82e63d4a15f7f62442bf733)

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