Add rdiff.md converted from rst
Add rdiff.md converted from rst

librsync/librsync,yrgoldteeth/librsync,librsync/librsync,sourcefrog/librsync,librsync/librsync,yrgoldteeth/librsync,sourcefrog/librsync,dbaarda/librsync,librsync/librsync,yrgoldteeth/librsync,yrgoldteeth/librsync,Salamek/librsync,sourcefrog/librsync,dbaarda/librsync,sourcefrog/librsync,dbaarda/librsync,Salamek/librsync,dbaarda/librsync,Salamek/librsync