Added section for extending a Connection.

docs/extending_core_components.asciidoc

@@ -3,7 +3,29 @@
 We decided to make this client low-level, and as such we probably have not implemented all the features you are looking for. For this reason, we made extending or even replacing the core components simple.
 
 === Connection
-Coming Soon
+Extending a connection provides the powerful ability to change requests as they go out to the ElasticSearch REST API.
+
+For example, you can extend the `HttpConnector` to force the default HTTP method to be `POST`:
+[source,js]
+---------------
+var elasticsearch = require('elasticsearch');
+var util = require('util');
+var HttpConnector = require('elasticsearch/src/lib/connectors/http');
+
+function MyHttpConnector(host, config) {
+  HttpConnector.call(this, host, config);
+}
+util.inherits(MyHttpConnector, HttpConnector);
+MyHttpConnector.prototype.makeReqParams = function(params) {
+  params = params || {};
+  params.method = params.method || 'POST';
+  returh HttpConnector.prototype.makeReqParams.call(this, params);
+};
+
+var client = new elasticsearch.Client({
+  connectionClass: MyHttpConnector
+});
+---------------
 
 === ConnectionPool
 Coming Soon