Add README

README.md

+# JupyterHub Authentication for the LabPop project
+
+## Dev
+
+It's recommended to have [uv][uv] installed, together with GNU make.
+
+Build the library wheel
+
+```
+make build
+```
+
+Build the dev docker image
+
+```
+make playground-image
+```
+
+Spawn a jupyterhub server on localhost:8000
+
+```
+make playground-run
+```
+
+The default database of users is at `./playground/testusers.json`, with passwords equal to the username.
+
+[uv]: https://github.com/astral-sh/uv