docs(derive): Link to ref from traits

This is to help with #3189

Cargo.toml

@@ -50,6 +50,7 @@ pre-release-replacements = [
   {file="CHANGELOG.md", search="<!-- next-url -->", replace="<!-- next-url -->\n[Unreleased]: https://github.com/clap-rs/clap/compare/{{tag_name}}...HEAD", exactly=1},
   {file="README.md", search="github.com/clap-rs/clap/blob/[^/]+/", replace="github.com/clap-rs/clap/blob/{{tag_name}}/", exactly=9, prerelease = true},
   {file="README.md", search="version = \"[a-z0-9\\.-]+\"", replace="version = \"{{version}}\"", exactly=1, prerelease = true},
+  {file="src/derive.rs", search="github.com/clap-rs/clap/blob/[^/]+/", replace="github.com/clap-rs/clap/blob/{{tag_name}}/", exactly=4, prerelease = true},
 ]
 
 [features]

src/derive.rs

@@ -19,6 +19,10 @@ use std::ffi::OsString;
 ///
 /// See also [`Subcommand`] and [`Args`].
 ///
+/// See the
+/// [derive reference](https://github.com/clap-rs/clap/blob/v3.0.0-rc.10/examples/derive_ref/README.md)
+/// for attributes and best practices.
+///
 /// **NOTE:** Deriving requires the `derive` feature flag
 ///
 /// # Examples
@@ -280,6 +284,10 @@ pub trait FromArgMatches: Sized {
 ///   `Args`.
 /// - `Variant(ChildArgs)`: No attribute is used with enum variants that impl `Args`.
 ///
+/// See the
+/// [derive reference](https://github.com/clap-rs/clap/blob/v3.0.0-rc.10/examples/derive_ref/README.md)
+/// for attributes and best practices.
+///
 /// **NOTE:** Deriving requires the `derive` feature flag
 ///
 /// # Example
@@ -320,6 +328,10 @@ pub trait Args: FromArgMatches + Sized {
 /// - `#[clap(flatten)] Variant(SubCmd)`: Attribute can only be used with enum variants that impl
 ///   `Subcommand`.
 ///
+/// See the
+/// [derive reference](https://github.com/clap-rs/clap/blob/v3.0.0-rc.10/examples/derive_ref/README.md)
+/// for attributes and best practices.
+///
 /// **NOTE:** Deriving requires the `derive` feature flag
 ///
 /// # Example
@@ -360,6 +372,10 @@ pub trait Subcommand: FromArgMatches + Sized {
 /// - Call [`Arg::possible_values`][crate::Arg::possible_values]
 /// - Allowing using the `#[clap(default_value_t)]` attribute without implementing `Display`.
 ///
+/// See the
+/// [derive reference](https://github.com/clap-rs/clap/blob/v3.0.0-rc.10/examples/derive_ref/README.md)
+/// for attributes and best practices.
+///
 /// **NOTE:** Deriving requires the `derive` feature flag
 ///
 /// # Example