Adds fallback site to docs, closes Raku#2911 after updating

README.md

@@ -2,7 +2,10 @@
 
 [![Build Status](https://travis-ci.org/perl6/doc.svg?branch=master)](https://travis-ci.org/perl6/doc) [![artistic](https://img.shields.io/badge/license-Artistic%202.0-blue.svg?style=flat)](https://opensource.org/licenses/Artistic-2.0) [![Run Status](https://api.shippable.com/projects/591e99923f2f790700098a30/badge?branch=master)](https://app.shippable.com/github/perl6/doc)
 
-An HTML version of this documentation can be found at [https://docs.perl6.org/](https://docs.perl6.org/).
+An HTML version of this documentation can be found
+at [https://docs.perl6.org/](https://docs.perl6.org/) and also
+at [`perl6docs.github.io`](https://perl6docs.github.io) (which is
+actually updated more frequently).
 This is currently the recommended way to consume the documentation.
 
 There is also a command line tool called `p6doc`, which you can use to