R4820 incorrect mention of the missing method Request::instance

Originally submitted by @Asenar in [R4820](http://dev.kohanaframework.org/issues/4820) and based on his PR #455

> Various place in guide and php comments were mentionning
Request::instance() to be used. I replaced it either by
Request::factory() or something more appropriate.

the file ` guide/kohana/routing.md ` in `3.3/develop` did not have the bottom part to fix.

Related to #547. Please review and merge.