UG edits: sdk chapter and app_support appx

- Wanted to remove the Documentation Feedback section from app_support
- The same information is already included in the Documentation first section.
- But it looks like something else refers to it, so it's back in.
- Patch Set 3: fixed sdk_neutron and app_support

Change-Id: Ibb19265e1ee79300dc02eeab35da45e64eee1a48
Merge "UG edits: sdk chapter and app_support appx"