tspd should have ability to inject specific section into readme

Right now, tspd will overwrite the entire readme.md file based on the options defined in $lib. It would be better if this appended the options (and any other docs) into the readme rather than overwriting. This would allow emitters to include more emitter-specific information in the readme that is not easily covered by tspd generation. Append vs overwrite could be an option in tspd.