docs: add code interface to generic actions guide

documentation/topics/actions/generic-actions.md

@@ -71,6 +71,7 @@ end
 > instance or instances of the resource. It's natural to assume that you can
 > set your action's return type to the name of your resource. This won't work
 > as resources do not define a type, unless they are embedded. In embedded resources, this won't work because the module is still being compiled, so referencing yourself as a type causes a compile error. Instead, use the `:struct` type and the `instance_of` constraint, like so:
+>
 > ```elixir
 > action :get, :struct do
 >   constraints instance_of: __MODULE__
@@ -108,4 +109,19 @@ Call this action:
 |> Ash.run_action()
 
 IO.puts(greeting)  # Output: Hello: Alice
-```
+```
+
+### Using Code Interface
+
+You can also use [Code Interfaces](documentation/topics/resources/code-interfaces.md) to call actions:
+
+Given a definition like:
+
+```elixir
+define :say_hello, args: [:name]
+```
+
+```elixir
+{:ok, greeting} = Resource.say_hello("Alice")
+greeting = Resource.say_hello!("Alice")
+```