Document corgi changes

Author: iarna

README.md

@@ -53,6 +53,19 @@ for authorization. These credentials always look the same:
 * `alwaysAuth` {Boolean} Whether calls to the target registry are always
   authed.
 
+## Requests
+
+As of `npm-registry-client@8`, all requests are made with an `Accept` header
+of `application/vnd.npm.install-v1+json; q=1.0, application/json; q=0.8, */*`.
+
+This enables filtered document responses to requests for package metadata.
+You know that you got a filtered response if the mime type is set to
+`application/vnd.npm.install-v1+json` and not `application/json`.
+
+This filtering substantially reduces the over all data size.  For example
+for `https://registry.npmjs.org/npm`, the compressed metadata goes from
+410kB to 21kB.
+
 ## API
 
 ### client.access(uri, params, cb)