README: link to RFC 7234 (#83)

Author: simon04

README.md

@@ -3,7 +3,7 @@ httpcache
 
 [![Build Status](https://travis-ci.org/gregjones/httpcache.svg?branch=master)](https://travis-ci.org/gregjones/httpcache) [![GoDoc](https://godoc.org/github.com/gregjones/httpcache?status.svg)](https://godoc.org/github.com/gregjones/httpcache)
 
-Package httpcache provides a http.RoundTripper implementation that works as a mostly RFC-compliant cache for http responses.
+Package httpcache provides a http.RoundTripper implementation that works as a mostly [RFC 7234](https://tools.ietf.org/html/rfc7234) compliant cache for http responses.
 
 It is only suitable for use as a 'private' cache (i.e. for a web-browser or an API-client and not for a shared proxy).