[Docs] Correct description of lldbinit behavior
Jim pointed out that "every time somebody has touched the documentation
on startup files they have stated that we source the application one and
then the global one, even though in actual fact we’ve never done that."
Indeed, when we read the application specific .lldbinit file, the global
one is not read. This patch updates the man page to reflect that.
(cherry picked from commit ac1dc1336ad76d719445d706654ca0ec4ff5557c)