Add missing `pid_file' setting in documenation.
Add missing `pid_file' setting in documenation.

facette/facette,vovkasm/facette,yonglehou/facette,vovkasm/facette,hirocaster/facette,githubert/facette,facette/facette,iaean/facette,Skrupellos/facette,vovkasm/facette,Skrupellos/facette,psytra/facette,iaean/facette,yonglehou/facette,hirocaster/facette,iaean/facette,githubert/facette,yonglehou/facette,psytra/facette,githubert/facette,facette/facette,facette/facette,hirocaster/facette,psytra/facette,Skrupellos/facette