message: [book] fix link to rustdoc
  mdbook is broken due to
diff: # Introduction
  -This page hosts specifications for some of the cryptographic algorithms of [Mina](https://minaprotocol.com/). [For the Rust documentation, see here](/rustdoc).
  +This page hosts specifications for some of the cryptographic algorithms of [Mina](https://minaprotocol.com/). [For the Rust documentation, see here](rustdoc).
  