CMake Nightly Date Stamp
Help: Document the CMAKE_TOOLCHAIN_FILE.

Link to the new docs from existing references to the variable.
Help: Document the CMAKE_FIND_ROOT_PATH* variables.

Add a replacement template for the variables, and link to them from
the documentation for the find_* commands.
Help: Add CMake manual for toolchain related docs.
Merge topic 'cmake-toolchains-manual' into next

0b2974d Help: Add CMake manual for toolchain related docs.
3e3f8b4 Help: Document the CMAKE_FIND_ROOT_PATH* variables.
531c108 Help: Document the CMAKE_TOOLCHAIN_FILE.
d05e0aa CMake Nightly Date Stamp