Adding a New Flight Mode to Copter

I read the developer documentation. I wrote the code and compiled it. There is no problem so far, but when I try to test the mode with SITL, I cannot see the mode. How can I overcome this problem?

Define “see” in great detail.

The my new mod is not available in SITL

You need to add the mode to mavproxy then.

Is there any documentation about this?