Readme: add links to the generated docs.

aslo add installation instructions for `rustfmt`

CONTRIBUTING.md

@@ -160,7 +160,7 @@ account from other OAuth services.
 [syntax]: gobject-notes/syntax.md
 [maintainer]: README.md#maintainers
 [internals]: doc-internals/src/SUMMARY.md
-[internals-rendered]: https://federico.pages.gitlab.gnome.org/gnome-class/
+[internals-rendered]: https://federico.pages.gitlab.gnome.org/gnome-class/book
 [mdbook]: https://github.com/rust-lang-nursery/mdBook
 [testing-strategy]: doc-internals/src/testing.md
 [gitlab]: https://gitlab.gnome.org/federico/gnome-class

README.md

@@ -16,6 +16,8 @@ The goal of this Gnome-class crate is to let you write GObject
 implementations in Rust with minimal or no boilerplate, and with
 compile-time type safety all along.
 
+The library API refference can be found **[here][class-docs]**
+
 ## Requirements
 
 Gnome-class is a Rust procedural macro.  We make use of some features
@@ -40,6 +42,14 @@ cargo +nightly test
 
 instead of the usual "`cargo test`" you would use for development.
 
+Gnome-class also depends on the `rustfmt` utility which can be easily
+installed with [`rustup`].
+
+```sh
+rustup component add rustfmt-preview
+```
+
+
 [`rustup`]: https://www.rustup.rs/
 
 ## How gnome-class works
@@ -143,3 +153,4 @@ ways:
 [mail]: mailto:federico@gnome.org
 [coc]: code-of-conduct.md
 [contributing]: CONTRIBUTING.md
+[class-docs]: https://federico.pages.gitlab.gnome.org/gnome-class/doc/gobject_gen/