Add documentation for creating "custom verbs" with Starlark macros
This was originally submitted as this is merely moving it to the normal docs site rather than the blog.
Closes
@@ -74,7 +74,8 @@ they will not be executed.
## Creating extensions
* [Create your first macro](tutorial-creating-a-macro.md) in order to reuse some
- code. Then [learn more about macros](macros.md).
+ code. Then [learn more about macros](macros.md) and
+ [using them to create "custom verbs"](tutorial-custom-verbs.md).
* [Follow the rules tutorial](rules-tutorial.md) to get started with rules.
Next, you can read more about the [rules concepts](rules.md).
