[CI] Re-add humble workflow files and add iron to readme (backport #818) (#820)

Author: mergify[bot]

.github/workflows/README.md

@@ -10,6 +10,7 @@ Commonly used and generalized controllers for ros2-control framework that are re
 ROS2 Distro | Branch | Build status | Documentation | Released packages
 :---------: | :----: | :----------: | :-----------: | :---------------:
 **Rolling** | [`rolling`](https://github.com/ros-controls/ros2_controllers/tree/rolling) | [![Rolling Binary Build](https://github.com/ros-controls/ros2_controllers/actions/workflows/rolling-binary-build-main.yml/badge.svg?branch=master)](https://github.com/ros-controls/ros2_controllers/actions/workflows/rolling-binary-build-main.yml?branch=master) <br /> [![Rolling Semi-Binary Build](https://github.com/ros-controls/ros2_controllers/actions/workflows/rolling-semi-binary-build-main.yml/badge.svg?branch=master)](https://github.com/ros-controls/ros2_controllers/actions/workflows/rolling-semi-binary-build-main.yml?branch=master) |  | [ros2_controllers](https://index.ros.org/p/ros2_controllers/#rolling)
+**Iron** | [`iron`](https://github.com/ros-controls/ros2_controllers/tree/iron) | [![Iron Binary Build](https://github.com/ros-controls/ros2_controllers/actions/workflows/iron-binary-build-main.yml/badge.svg?branch=master)](https://github.com/ros-controls/ros2_controllers/actions/workflows/iron-binary-build-main.yml?branch=master) <br /> [![Iron Semi-Binary Build](https://github.com/ros-controls/ros2_controllers/actions/workflows/iron-semi-binary-build-main.yml/badge.svg?branch=master)](https://github.com/ros-controls/ros2_controllers/actions/workflows/iron-semi-binary-build-main.yml?branch=master) |  | [ros2_controllers](https://index.ros.org/p/ros2_controllers/#iron)
 **Humble** | [`humble`](https://github.com/ros-controls/ros2_controllers/tree/humble) | [![Humble Binary Build](https://github.com/ros-controls/ros2_controllers/actions/workflows/humble-binary-build-main.yml/badge.svg?branch=master)](https://github.com/ros-controls/ros2_controllers/actions/workflows/humble-binary-build-main.yml?branch=master) <br /> [![Humble Semi-Binary Build](https://github.com/ros-controls/ros2_controllers/actions/workflows/humble-semi-binary-build-main.yml/badge.svg?branch=master)](https://github.com/ros-controls/ros2_controllers/actions/workflows/humble-semi-binary-build-main.yml?branch=master) |  | [ros2_controllers](https://index.ros.org/p/ros2_controllers/#humble)
 
 ### Explanation of different build types

README.md

@@ -0,0 +1,6 @@
+repositories:
+  ## EXAMPLE DEPENDENCY
+#   <some_ros_package>:
+#     type: git
+#     url: [email protected]:<some_github_namespace>/<some_ros_package>.git
+#     version: master