Add How To documentation

The IMM defines the following How-To documentation categories:

- [ ] Common scenarios
- [ ] Extensibility Scenarios
- [ ] End to end integration (with other IP)

Being inherently "connective tissue" this doesn't exactly have extensibility scenarios of its own, so it's not clear whether we can do much for the middle one. But the other two are certainly possible. When picking these off, add individual work items for each, and reference them from here - this issue is primarily to track progress on getting up to speed on the IMM.