update CHANGELOG.md

Author: nwh

CHANGELOG.md

@@ -12,6 +12,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Start testing on PyPy. Due to [#342](https://github.com/PyFilesystem/pyfilesystem2/issues/342)
   we have to treat PyPy builds specially and allow them to fail, but at least we'll
   be able to see if we break something aside from known issues with FTP tests.
+- Added `readinto` method for `MemoryFS` file objects
+  [#380](https://github.com/PyFilesystem/pyfilesystem2/issues/380).
 
 ## [2.4.11] - 2019-09-07