Add "Using CSP with a CDN"

Thanks to Ryan Cannon for this!

README.md

@@ -97,3 +97,8 @@ app.use(function (req, res) {
   res.end('<script nonce="' + res.locals.nonce + '">alert(1 + 1);</script>')
 })
 ```
+
+Using CSP with a CDN
+--------------------
+
+The default behavior of CSP is generate headers tailored for the browser that's requesting your page. If you have a CDN in front of your application, the CDN may cache the wrong headers, rendering your CSP useless. Make sure to eschew a CDN when using this module or set the `browserSniff` option to `false`.

package.json

@@ -2,7 +2,8 @@
   "name": "helmet-csp",
   "author": "Adam Baldwin <baldwin@andyet.net> (http://andyet.net/team/baldwin)",
   "contributors": [
-    "Evan Hahn <me@evanhahn.com> (http://evanhahn.com)"
+    "Evan Hahn <me@evanhahn.com> (http://evanhahn.com)",
+    "Ryan Cannon <ryan@ryancannon.com> (https://ryancannon.com)"
   ],
   "description": "Content Security Policy middleware.",
   "version": "1.0.3",