Add some user documentation

[David Aspinall <da+pgtrac@…>]

We need some user-level documentation to include in the product. It doesn't need to be extensive but should point out the Proof General-specific features we have supplied and outline how to use them. Main goals:

• help people find the useful features they may not realise are available;
• explain things about using them that might be unobvious or not easily discovered

Of course, (most) people don't read documentation and expect to find their way around without consulting it so we should think how to make anything non-obvious easier!

Let's use this ticket to gather some examples. Screenshots are also useful.

[David Aspinall]

Milestone PG-Eclipse-1.1.0 deleted