Clear instructions for preparing bundle help files

[Tristan Croll]

I may have just missed it, but the instructions on how to make a bundle play nicely with ChimeraX's help viewer (i.e. bring up the right help file when a user right-clicks on the tool widget and clicks "Help) don't appear to be in the "Building and distributing bundles" instructions. I worked it out in the end by tracing through code and now I know how I see it's absurdly easy - just put it in a directory called "docs" in the bundle path (I had it in "doc"). I think it would be a good idea to add a paragraph or two on this to the online developer instructions.

[Eric Pettersen]

This is in fact covered in the tutorial. I'll put in some kind of cross reference.