Nested Usage Help Text

**Feature Request**

**Description**
As I am learning to use taskwarrior, I find myself repeatedly referring to the usage text output of the `help` command. Making the output of this command nested, in the sense that it lists topics that I can call `help` on to get usage specific to the command or concept, would make parsing the usage text much easier on the user.

**Solution**
Create a nested usage help menu.

**Additional context**
Here's an example of the kind of nested usage help text I'm talking about, taken from Arch's package manager: