Add "help" button in GUI profile editor

[fenugrec]

Hi, great software so far, one minor addition I would like to see is simply a way to access the documentation while working in the profile editor. Use case : while editing additional parameters, some of them refer to certain sections in the documentation, which require to

1. cancel editing the current parameter
2. "open" any profile, and let it run
3. finally, go to Help->Basic Concepts etc.

[bcpierce00]

Happy to accept a patch.

[fenugrec]

I did consider it - gave up when I saw how the Help menu is autogenerated from the docs, and didn't see a clean way of creating a button that links to a specific doc section.

For anyone interested in looking at this (gtk2-specific, didn't check others)

• help menu is created in (let addDocSection ...) https://github.com/bcpierce00/unison/blob/master/src/uigtk2.ml#L3418
• the Doc sections are generated here (let documentation sect = ...)https://github.com/bcpierce00/unison/blob/master/src/uigtk2.ml#L2514
• Profile Editor (editProfile) window is created here https://github.com/bcpierce00/unison/blob/master/src/uigtk2.ml#L2065