docs: add pandoc dependency

.github/workflows/build-docs-tests.yml

@@ -21,6 +21,7 @@ jobs:
           python-version: 3.12
       - name: "Test doc"
         run: |
+          sudo apt-get install pandoc
           python3 -m pip install --upgrade pip setuptools
           pip install .[docs,recommended]
           cd ./docs

docs/community/community.md

@@ -58,7 +58,11 @@ npm run js-test
 
 ### Check that the documentation still builds
 
+You'll need `pandoc`, see https://pandoc.org/installing.html
+Then,
+
 ```sh
+pip install .[docs]
 cd docs
 make clean html
 ```