Add sphinx-autobuild to gitpod setup

.gitpod.yml

@@ -1,9 +1,10 @@
 tasks:
   - init: |
+      pip3 install sphinx-autobuild
       pip3 install -r docs/doc-requirements.txt
       pip3 install -e.
     command: |
-      cd docs && make html &&  cd build/html && python3 -m http.server 8080
+      sphinx-autobuild docs/source/ docs/build/html/
     name: Sphinx preview
 ports:
-- port: 8080
+- port: 8000