Added change log

Author: Nyholm

CHANGELOG.md

@@ -3,6 +3,15 @@
 Starting with version 5, the Facebook PHP SDK follows [SemVer](http://semver.org/).
 
 
+## 6.x
+
+
+- 6.0 (201?-??-??)
+  - We use an HTTP client abstraction called HTTPlug to give the user more control over *how* to send PSR7 messages. See updated installation instructions. 
+  - Removed option `http_client_handler`
+  - Added option `http_client` which should be an object implementing `\Http\Client\HttpClient`
+  - Removed functions `FacebookClient::setHttpClientHandler()` and `FacebookClient::getHttpClientHandler()` in favor for `FacebookClient::getHttpClient()` and `FacebookClient::setHttpClient()`.
+
 ## 5.x
 
 Version 5 of the Facebook PHP SDK is a complete refactor of version 4. It comes loaded with lots of new features and a friendlier API.