Equality: add examples to docstring

Show effect of simplify and evaluate=False kwarg.

(one of several bits left over from #7960, if unwanted just say so).
> The default is to attempt evaluation. An unevaluated Equality will
> be returned if nothing is trivially apparent about the relationship.

Are you sure?  There is a paragraph there already.   I could reword it to be more like this version if you like...