message: update docs
  [ci skip]
diff: @@ -1814,10 +1814,10 @@ OSPRay in MPI mode:
  Enabling the MPI module in your build
  -------------------------------------
  -To build the MPI module the CMake variable `OSPRAY_MODULE_MPI` must be
  -enabled, which can be done directly on the command line (with `-D...`)
  -or through a configuration dialog (`ccmake`, `cmake-gui`), see also
  -\[Compiling OSPRay\].
  +To build the MPI module the CMake variable `OSPRAY_MODULE_MPI=ON` must
  +be enabled, which can be done directly on the command line (with
  +`-D...`) or through a configuration dialog (`ccmake`, `cmake-gui`), see
  +also [Compiling OSPRay](#compiling-ospray).
  This will trigger CMake to go look for an MPI implementation in your
  environment. You can then inspect the CMake value of `MPI_LIBRARY` to
  