docs: Integrate with readthedocs.org

This patch adds configuration to integrate with readthedocs.org, using
mkdocs as rendering engine.

It also does minor documentation updates, to tidy some things up
(clearer titles, move some documentation from the root into docs/, etc).

docs/index.md

@@ -0,0 +1,24 @@
+
+# chasquid
+
+[chasquid](https://blitiri.com.ar/p/chasquid) is an SMTP (email) server with a
+focus on simplicity, security, and ease of operation.
+
+This is the documentation index.
+
+Please see the [project page](https://blitiri.com.ar/p/chasquid) for more
+details.
+
+
+## Contact
+
+If you have any questions, comments or patches please send them to the [mailing
+list](https://groups.google.com/forum/#!forum/chasquid),
+chasquid@googlegroups.com.
+
+To subscribe, send an email to chasquid+subscribe@googlegroups.com.
+
+You can also reach out via IRC, `#chasquid` on
+[freenode](https://freenode.net/).
+
+