message: added graphviz dependency
diff: @@ -123,11 +123,11 @@ all share the same subscriptions and therefore recieve the same data.
  ## Generate Documentation
  You can generate a doxygen documentation page for the GDS source.
  -To do this, you will need to install `doxygen` and `doxypypy`.
  +To do this, you will need to install `doxygen`, `doxypypy` and `graphviz`.
  ### Linux/Windows WSL
  ```
  -apt-get install doxygen
  +apt-get install doxygen graphviz
  pip install doxypypy
  ```
  @@ -135,6 +135,7 @@ pip install doxypypy
  Install doxygen from the website (http://www.stack.nl/~dimitri/doxygen/download.html) or by using the following command if you have Homebrew
  ```
  brew install doxygen
  +brew install graphviz
  pip install doxypypy
  ```
  