Add readme

README.md

+# Jupyterhub interactive environment with CbmRoot
+
+## Set up
+Pull image from registry:
+* CERN:
+```bash
+docker login -u ${USER} gitlab-registry.cern.ch
+docker pull gitlab-registry.cern.ch/elavrik/cbmroot-hub
+```
+* Docker hub:
+```bash
+docker pull elavrik/cbmroot-hub
+```
+
+## Run
+
+With docker cli
+`docker run -it -p 8000:8000 elavrik/cbmroot-hub`
+
+With docker-compose
+`docker-compose up -d cbmroot-hub`
+
+Navigate with your browser to `https://localhost:8000`
+use default login `user` and password `test` to start the session.