Action example guide

[qiuzhong]

The action feature is implemented and an action client/server example is added. However, to execute this example, a colcon build command should be executed for ros1_action and generate some .so files for the customized action file.

There should be a detailed guide to instruct how to make it step by step.

[qiuzhong]

As #376 merged, I think this issue can be closed now.