Replace original docs README.txt

We need something that points back to the code now.

docs/README.md

@@ -0,0 +1,7 @@
+# LibreTime Documentation
+
+The LibreTime documentation is created from this directory using `mkdocs`. You may read 
+it at [libretime.org](http://libretime.org).
+
+The canonical source of this documentation is in the [LibreTime repo](https://github.com/LibreTime/libretime)
+in the [`docs/` subdir](https://github.com/LibreTime/libretime/tree/master/docs).