Guide: `&mut self` `self` do not have examples

[gamazeps]

In the 'Method syntax' section, three syntaxes are mentioned: self, &self, and &mut self.
However only the &self syntax is given an example.

I think it may be usefull to give some sample code using the other syntaxes.

It should be rather easy and a good first issue if someone wants to start working on Rust :)

[steveklabnik]

There's now &mut self but no self.

[jxcl]

@steveklabnik I'd like to write a section in Method Syntax detailing self, &self and &mut self a bit more, with explicit examples of when you would use each of them and that reinforces the idea that if you use self then ownership of self will be transferred into that scope and will be destroyed if not returned. Thoughts?

[steveklabnik]

That'd be great.