KDEGitCommitHooks: Check if KDEClangFormat was included
If the module is not included, the current message would be misleading.
Including the module by default is undesirable, because we print out a warning that we do not override an existing module. While this warning is reasonable in most cases, it is annoying for projects that have a custom clang-format file.
Checking if a .clang-format file exists and if not including KDEClangFormat is fragile, because it depends on the include order of the modules.
Considering all that, a proper warning with instructions on how to fix the issue is IMHO the best way to go.