message: memo: release mode in building doc
diff: @@ -8,9 +8,9 @@ you to build project/make files for any platform. For details on `cmake`, see
  <https://www.cmake.org>. In brief, depending on your platform, use one of
  e.g.:
  - cmake -G "Unix Makefiles"
  - cmake -G "Visual Studio 10"
  - cmake -G "Xcode"
  + cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Release
  + cmake -G "Visual Studio 10" -DCMAKE_BUILD_TYPE=Release
  + cmake -G "Xcode" -DCMAKE_BUILD_TYPE=Release
  Then, build as normal for your platform. This should result in a `flatc`
  executable, essential for the next steps.
  