update the docs

Author: yzeng

.github/workflows/docs.yml

@@ -19,6 +19,8 @@ jobs:
       - name: Dependencies
         run: |
           echo "Installing python packages for docs..."
+          sudo apt-get update
+          sudo apt-get install -y doxygen         
           python3 -m pip install --upgrade pip
           python3 -m pip install sphinx sphinx_rtd_theme breathe sphinxcontrib.bibtex docutils