docs: Describe the example we show

This also provides us another opportunity to link to the docs.

Author: epage

Cargo.toml

@@ -51,7 +51,7 @@ pre-release-replacements = [
   {file="CHANGELOG.md", search="ReleaseDate", replace="{{date}}", min=1},
   {file="CHANGELOG.md", search="<!-- next-header -->", replace="<!-- next-header -->\n## [Unreleased] - ReleaseDate\n", exactly=1},
   {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="github.com/clap-rs/clap/blob/[^/]+/", replace="github.com/clap-rs/clap/blob/{{tag_name}}/", exactly=10, 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},
 ]

README.md

@@ -31,6 +31,10 @@ Create your command-line parser, with all of the bells and whistles, declarative
 
 ### Example
 
+This uses our
+[Derive API](https://github.com/clap-rs/clap/blob/v3.0.10/examples/derive_ref/README.md)
+which provides access to the Builder API as attributes on a `struct`:
+
 <!-- Copied from examples/demo.{rs,md} -->
 ```rust,no_run
 use clap::Parser;