docs(readme): Clarify what source we refer to

Author: epage

README.md

@@ -7,7 +7,7 @@ A straightforward static site generator written in [Rust](http://www.rust-lang.o
 
 ## Documentation
 
-- [User documentation](https://cobalt-org.github.io/) and [source](https://github.com/cobalt-org/cobalt-org.github.io)
+- [User documentation](https://cobalt-org.github.io/) ([website source](https://github.com/cobalt-org/cobalt-org.github.io))
 - [API documentation](https://docs.rs/cobalt-bin)
 - [Contributing](https://github.com/cobalt-org/cobalt.rs/blob/master/CONTRIBUTING.md)
 - [LICENSE](https://github.com/cobalt-org/cobalt.rs/blob/master/LICENSE-MIT)