radicle: document `parse_ref` and `parse_ref_namespaced` — heartwood

Provide better documentation for the two methods.

Solves the issue:

rad inbox 4603f55d97a0776f37bae2f9d2ba7d455d8a4c83

     Ok(remotes)
 }
 /// Parse a ref string. Returns an error if it isn't namespaced.
 /// Parse a [`format::Qualified`] reference string while expecting the reference
 /// to start with `refs/namespaces`. If the namespace is not present, then an
 /// error will be returned.
 ///
 /// The namespace returned is the path component that is after `refs/namespaces`,
 /// e.g. in the reference below, the segment is
 /// `z6MkvUJtYD9dHDJfpevWRT98mzDDpdAtmUjwyDSkyqksUr7C`:
 ///
 ///     refs/namespaces/z6MkvUJtYD9dHDJfpevWRT98mzDDpdAtmUjwyDSkyqksUr7C/refs/heads/main
 ///
 /// The `T` can be specified when calling the function. For example, if you
 /// wanted to parse the namespace as a `PublicKey`, then you would the function
 /// like so, `parse_ref::<PublicKey>(s)`.
 pub fn parse_ref_namespaced<T>(s: &str) -> Result<(T, format::Qualified), RefError>
 where
     T: FromStr,

     }
 }
 /// Parse a ref string. Optionally returns a namespace.
 /// Parse a [`format::Qualified`] reference string. It will optionally return
 /// the namespace, if present.
 ///
 /// The qualified form could be of the form: `refs/heads/main`,
 /// `refs/tags/v1.0`, etc.
 ///
 /// The namespace returned is the path component that is after `refs/namespaces`,
 /// e.g. in the reference below, the segment is
 /// `z6MkvUJtYD9dHDJfpevWRT98mzDDpdAtmUjwyDSkyqksUr7C`:
 ///
 ///     refs/namespaces/z6MkvUJtYD9dHDJfpevWRT98mzDDpdAtmUjwyDSkyqksUr7C/refs/heads/main
 ///
 /// The `T` can be specified when calling the function. For example, if you
 /// wanted to parse the namespace as a `PublicKey`, then you would the function
 /// like so, `parse_ref::<PublicKey>(s)`.
 pub fn parse_ref<T>(s: &str) -> Result<(Option<T>, format::Qualified), RefError>
 where
     T: FromStr,