Docs site (#269)

* Set up documentation site using jekyll

* Add workflow for deploying docs

* Ini formatting is hard to read

* Add instructions on how to run docs locally

* Work through docs

* Remove content from README

* Miscellaneous fixes

* Fix artifact upload

docs/how-tos/use-rootless-docker.md

@@ -0,0 +1,23 @@
+---
+title: Use with rootless Docker
+layout: default
+parent: How Tos
+nav_order: 15
+---
+
+# Use with rootless Docker
+
+It's also possible to use this image with a [rootless Docker installation][rootless-docker].
+Instead of mounting `/var/run/docker.sock`, mount the user-specific socket into the container:
+
+```yml
+services:
+  backup:
+    image: offen/docker-volume-backup:v2
+    # ... configuration omitted
+    volumes:
+      - backup:/backup:ro
+      - /run/user/1000/docker.sock:/var/run/docker.sock:ro
+```
+
+[rootless-docker]: https://docs.docker.com/engine/security/rootless/