Add --build-type ament_cmake to action tutorial

source/Tutorials/Intermediate/Creating-an-Action.rst

@@ -49,23 +49,32 @@ Tasks
 
       $ mkdir -p ~/ros2_ws/src # you can reuse an existing workspace with this naming convention
       $ cd ~/ros2_ws/src
-      $ ros2 pkg create --license Apache-2.0 custom_action_interfaces
+      $ ros2 pkg create --build-type ament_cmake --license Apache-2.0 custom_action_interfaces
 
   .. group-tab:: macOS
 
     .. code-block:: console
 
       $ mkdir -p ~/ros2_ws/src
       $ cd ~/ros2_ws/src
-      $ ros2 pkg create --license Apache-2.0 custom_action_interfaces
+      $ ros2 pkg create --build-type ament_cmake --license Apache-2.0 custom_action_interfaces
 
   .. group-tab:: Windows
 
     .. code-block:: console
 
       $ md \ros2_ws\src
       $ cd \ros2_ws\src
-      $ ros2 pkg create --license Apache-2.0 custom_action_interfaces
+      $ ros2 pkg create --build-type ament_cmake --license Apache-2.0 custom_action_interfaces
+
+``custom_action_interfaces`` is the name of the new package.
+Note that it is, and can only be, a CMake package, but this doesn't restrict in which type of packages you can use your actions.
+You can create your own custom interfaces in a CMake package, and then use it in a C++ or Python node.
+
+.. note::
+
+  It is good practice to keep ``.msg``, ``.srv``, and ``.action`` files in separate packages from the nodes that use them.
+  This makes it easier to reuse the interface definitions across different packages.
 
 
 2 Defining an action