Help: CMP0135 applies to FetchContent as well
This updates the CMP0135 documentation, which should have been done as part of c2044fdf (FetchContent: Respect the CMP0135 policy setting, 2022-06-02).
Originally pointed out in the forums here: https://discourse.cmake.org/t/fetchcontent-cmp0135/10422
Issue: #23560 (closed)