docs: create README

README.md

+# Conformance IdP deployment
+
+To easily run the conformance IdP, you can use docker compose:
+
+```shell
+cd docker
+docker compose up -d --build
+```
+
+This will start SimpleSAMLphp at `http://localhost/simplesaml/module.php/admin` with the conformance module installed,
+mariaDB database and nginx as a reverse proxy.
+
+You need to mount configuration and metadata folders, see `docker-compose.yml`, and add HTTPS (e.g. Let's encrypt).