If you have no protoc, you'll get the following error:
Doing "mvn test" or "mvn install", etc. yields:
[ERROR] Failed to execute goal com.github.igor-petruk.protobuf:protobuf-maven-plugin:0.6.3:run (default) on project common: Cannot execute 'protoc': Cannot run program "protoc": error=2, No such file or directory -> [Help 1]
Tell people what to do if they have this problem
Also note what happens if you have the wrong protoc.