add README.md with sphinx-autobuild

doc/README.md

+# https://hub.pages.pasteur.fr/strass/index.html
+
+# How to work in it
+
+Quick setup
+```sh
+cd docs
+virtualenv .venv -p python3
+source .venv/bin/activate
+pip install -r requirements.txt
+```
+
+And then you are able to host the doc locally to directly see your changes (at each save).
+To do so, use:
+
+```sh
+sphinx-autobuild . build/html --port 8044
+```