github: actions: Ensure warning free docs build

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>

.github/workflows/main.yml

@@ -38,7 +38,8 @@ jobs:
       id: install-packages
       run:  |
           sudo apt-get update
-          sudo apt-get install -y python3-sphinx python3-recommonmark python3-cryptography python3-cbor
+          sudo apt-get install -y python3-sphinx python3-cryptography python3-cbor graphviz
+          sudo pip3 install recommonmark
 
     - name: Update submodules
       id:   update-submodules

docs/appguide.rst

@@ -379,7 +379,7 @@ section to add an import and register for you application from ``main.py``
     then be patched into the system. For example the following can be used
     to adopt a new version of the CST816S driver:
 
-    .. code-block::
+    .. code-block:: sh
 
         ./tools/wasptool\
             --exec wasp/drivers/cst816s.py\