message: Add intra links for unstable features doc
diff: //! The steps for adding new Cargo.toml syntax are:
  //!
  //! 1. Add the cargo-features unstable gate. Search below for "look here" to
  -//! find the `features!` macro and add your feature to the list.
  +//! find the `features!` macro invocation and add your feature to the list.
  //!
  //! 2. Update the Cargo.toml parsing code to handle your new feature.
  //!
  //!
  //! 1. Add the option to the [`CliUnstable`] struct below. Flags can take an
  //! optional value if you want.
  -//! 2. Update the [`CliUnstable::add`][CliUnstable] function to parse the flag.
  +//! 2. Update the [`CliUnstable::add`] function to parse the flag.
  //! 3. Wherever the new functionality is implemented, call
  -//! [`Config::cli_unstable`][crate::util::config::Config::cli_unstable] to
  -//! get an instance of `CliUnstable` and check if the option has been
  -//! enabled on the `CliUnstable` instance. Nightly gating is already
  -//! handled, so no need to worry about that.
  +//! [`Config::cli_unstable`] to get an instance of [`CliUnstable`]
  +//! and check if the option has been enabled on the [`CliUnstable`] instance.
  +//! Nightly gating is already handled, so no need to worry about that.
  //!
  //! ## Stabilization
  //!
  //!
  //! 1. Update the feature to be stable, based on the kind of feature:
  //! 1. `cargo-features`: Change the feature to `stable` in the `features!`
  -//! macro below, and include the version and a URL for the documentation.
  -//! 2. `-Z unstable-options`: Find the call to `fail_if_stable_opt` and
  +//! macro invocation below, and include the version and a URL for the
  +//! documentation.
  +//! 2. `-Z unstable-options`: Find the call to [`fail_if_stable_opt`] and
  //! remove it. Be sure to update the man pages if necessary.
  -//! 3. `-Z` flag: Change the parsing code in [`CliUnstable::add`][CliUnstable]
  -//! to call `stabilized_warn` or `stabilized_err` and remove the field from
  -//! `CliUnstable. Remove the `(unstable)` note in the clap help text if
  +//! 3. `-Z` flag: Change the parsing code in [`CliUnstable::add`] to call
  +//! `stabilized_warn` or `stabilized_err` and remove the field from
  +//! [`CliUnstable`]. Remove the `(unstable)` note in the clap help text if
  //! necessary.
  //! 2. Remove `masquerade_as_nightly_cargo` from any tests, and remove
  //! `cargo-features` from `Cargo.toml` test files if any. You can
  //! 3. Update the docs in unstable.md to move the section to the bottom
  //! and summarize it similar to the other entries. Update the rest of the
  //! documentation to add the new feature.
  +//!
  +//! [`Config::cli_unstable`]: crate::util::config::Config::cli_unstable
  +//! [`fail_if_stable_opt`]: CliUnstable::fail_if_stable_opt
  use std::collections::BTreeSet;
  use std::env;
  