message: cmake: a bit of documentation
diff: @@ -5,6 +5,13 @@ import os
  class CMakeBuilder(drake.Builder):
  def __init__(self, cxx_toolkit, srcs, dsts, vars,
  targets = None, path_to_cmake_source = None):
  + '''
  + `srcs`: what we depend upon.
  + `dsts`: what will be built.
  + `vars`: dict variables passed to cmake via `-D`.
  + `targets`: list of Makefile targets.
  + `path_to_cmake_source`: path to the direction containing the CMakeFile.
  + '''
  self.__vars = vars
  self.__prefix = drake.Drake.current.prefix
  self.__path_to_cmake_source = \
  