CMake FetchContent documentation should specify GIT_SUBMODULES_RECURSE

[andrewkcorcoran]

The documentation for using the library with submodules specifies that you shouldn't recurse submodules for normal consumption. The documentation for using the library with CMake FetchContent omits this detail and doesn't mention that from CMake 3.17 you can disable FetchContent submodule recursion using the GIT_SUBMODULES_RECURSE option (which will get forwarded from FetchContent to https://cmake.org/cmake/help/latest/module/ExternalProject.html#id1)

[marzer]

Oh, it's actually much simpler than that; the documentation note about submodules is wrong and should be deleted. I moved away from using git submodules quite a while ago and I guess I forgot to delete that note at the time.

Thanks for bringing it to my attention, though!