finagle docs: Add response classification to user guide
finagle docs: Add response classification to user guide

Response classification is an important tool for client configuration
and should be covered in the user guide.

RB_ID=788240

koshelev/finagle,liamstewart/finagle,twitter/finagle,twitter/finagle,spockz/finagle,luciferous/finagle,koshelev/finagle,koshelev/finagle,lukiano/finagle,sveinnfannar/finagle,BuoyantIO/finagle,BuoyantIO/finagle,BuoyantIO/finagle,twitter/finagle,lukiano/finagle,spockz/finagle,luciferous/finagle,BuoyantIO/finagle,liamstewart/finagle,twitter/finagle,twitter/finagle,spockz/finagle,sveinnfannar/finagle,adriancole/finagle,mkhq/finagle,mkhq/finagle,adriancole/finagle,sveinnfannar/finagle,luciferous/finagle,lukiano/finagle,lukiano/finagle,spockz/finagle,koshelev/finagle,mkhq/finagle,spockz/finagle,spockz/finagle,mkhq/finagle,koshelev/finagle,sveinnfannar/finagle,adriancole/finagle,liamstewart/finagle,liamstewart/finagle,luciferous/finagle,adriancole/finagle,luciferous/finagle,lukiano/finagle,adriancole/finagle,lukiano/finagle,BuoyantIO/finagle,sveinnfannar/finagle,mkhq/finagle,BuoyantIO/finagle,luciferous/finagle,mkhq/finagle,adriancole/finagle,sveinnfannar/finagle,liamstewart/finagle,koshelev/finagle