(docs) Deprecation notice

@reem, <https://github.com/iron/static> is already created, with a [PR](https://github.com/iron/static/pull/1) queued.

Changing the name to `static` means that the crate needs to be imported using `extern crate "static" as static_file;`, as `static` is a reserved keyword. Seeing as this is detrimental to ergonomics, I didn't want to just push these changes, so they are queued in this and [that](https://github.com/iron/static/pull/1) pull requests.

Let's keep discussion on the namechange _here_, and ignore the other repository for now until we pull the trigger.
Thoughts? Anybody?