Document OATH requirement
OATH is now required; it isn't mentioned in the README as a dependency, and there's no documentation in the CMakeLists.txt why it's there or what it is for. It would be nice to replace the
find_package(... REQUIRED) by a non-required find along with suitable package properties. Then the
feature_summary() can do the right thing and users / packagers / whoever can deal with it more easily.