Documentation enhancements (#207)

This PR addresses the issue listed in issue #170 regarding how to set up rootless Docker. It also expands on the documentation to show how to create deployments for different environments.

Co-authored-by: ccureau <ccureau@noreply.gitea.io>
Reviewed-on: https://gitea.com/gitea/act_runner/pulls/207
Reviewed-by: Jason Song <i@wolfogre.com>
Co-authored-by: Chris Cureau <cmcureau@gmail.com>
Co-committed-by: Chris Cureau <cmcureau@gmail.com>

examples/docker-compose/README.md

@@ -0,0 +1,20 @@
+### Running `act_runner` using `docker-compose`
+
+```yml
+...
+  gitea:
+    image: gitea/gitea
+    ...
+
+  runner:
+    image: gitea/act_runner
+    restart: always
+    depends_on:
+      - gitea
+    volumes:
+      - ./data/act_runner:/data
+      - /var/run/docker.sock:/var/run/docker.sock
+    environment:
+      - GITEA_INSTANCE_URL=<instance url>
+      - GITEA_RUNNER_REGISTRATION_TOKEN=<registration token>
+```