Added CHANGELOG for #90

Author: weierophinney

CHANGELOG.md

@@ -8,12 +8,17 @@ All notable changes to this project will be documented in this file, in reverse
 
 - [#88](https://github.com/zendframework/zend-diactoros/pull/88) updates the
   `SapiEmitter` to emit a `Content-Length` header with the content length as
-  reported by the response body stream.
+  reported by the response body stream, assuming that
+  `StreamInterface::getSize()` returns an integer.
 - [#77](https://github.com/zendframework/zend-diactoros/pull/77) adds a new
   response type, `Zend\Diactoros\Response\TextResponse`, for returning plain
   text responses. By default, it sets the content type to `text/plain;
   charset=utf-8`; per the other response types, the signature is `new
   TextResponse($text, $status = 200, array $headers = []`.
+- [#90](https://github.com/zendframework/zend-diactoros/pull/90) adds a new
+  `Zend\Diactoros\CallbackStream`, allowing you to back a stream with a PHP
+  callable (such as a generator) to generate the message content. Its
+  constructor accepts the callable: `$stream = new CallbackStream($callable);`
 
 ### Deprecated