[documentation](inline-layout&contributing):

Expand documentation in several points of inline layout. Add
contributing to the servo-book section

Signed-off-by: Desiatkin Dmitrii <d.desyatkin@innopolis.university>

Author: d-desiatkin

src/SUMMARY.md

@@ -6,6 +6,7 @@
 - [Running servoshell](running-servoshell.md)
 - [Contributing to Servo\*](contributing.md)
   - [Requesting crate releases](hacking/requesting-crate-releases.md)
+  - [Contributing to this book](hacking/contributing-to-servo-book.md)
 
 # Hacking on Servo