Add description of jobset inputs in the 'Edit jobset' page

[rbvermaa]

For new users it would be good to have some documentation on the page itself available when entering jobset inputs. Perhaps include some examples per type of input as well.

[Baughn]

That would be nice. Right now I'm trying to add a Git input of https://github.com/Erisia/builder.git, and on pressing 'apply changes' it just disappears.