Documentation updates in commit 02f527c6 (Find: Provide global
controls for the `NO_[]_PATH` call options, 2019-06-12,
v3.16.0-rc1~541^2) accidentally switched the `find_library`
documentation to mention `INCLUDE` where it should be `LIB`.

While at it, update `find_file` and `find_path` to mention
`INCLUDE` and `PATH` in the order they are considered.