[mkgmap-dev] build instructions and protobuf

I'm glad to see pbf support in mkgmap, but doing an svn checkout and 'ant dist' fails, or at least prints an error. The README does not explain where to find the apparently missing jar files, or how to check them out and build them. Ideally, it would look in the system standard paths, so that one could install the jar with a 3rd-party package manager, and also look in ../protobuf/dist/protobuf.jar so that a parallel build of the other packages would get picked up. I can write a patch for README if someone sends a few hints, or I may get to searching. (sorry if I missed a mailinglist post, but this belongs in the sources. also I didn't find anhything on the buidling page of the wiki)