Update Changelog for v15.5.1-15.5.4

This could really use extra code review attention since the history of
these changes was a bit convoluted to follow.

After talking to @bvaughn and @acdlite, we thought it might make sense
to put the 'add-ons' changes in a separate change log. The other option,
of including them in the main React change log, seemed the more
confusing of the two.

Also this commit is related to and somewhat blocked by
facebook/prop-types#40

**what is the change?:**
Adding the change log for recent patch versions of React.

**why make this change?:**
We missed this step in the flurry of releasing patches, and it's useful
for folks who want info about what version to use.

**test plan:**
Visual inspection of the change log.

**issue:**
facebook#9443

ADD-ONS-CHANGELOG.md

@@ -0,0 +1,59 @@
+# React Add-Ons Change Log
+
+As of React v15.5.0 we discontinued active maintenance of the React Addons
+packages. In previous versions of React we kept the version numbers of
+these packages in sync with the React version, and included updates to
+them in the main React `CHANGELOG.md`.
+
+Since the release versions of these packages are now out of sync with React,
+and we are no longer including them as a supported part of React, we have split
+out the latest changes into this separate change log.
+
+## Create Fragment
+
+### 15.5.3
+
+* Fix react-addons-create-fragment package to export correct thing. [See #9383](https://github.com/facebook/react/pull/9383).
+* Envify and collapse create-fragment UMD. [See #9383](https://github.com/facebook/react/pull/9383).
+
+## Create-React-Class
+
+### 15.5.2
+
+* Fix devDeps. [See #9383](https://github.com/facebook/react/pull/9383).
+* Add missing object-assign dependency. [See #9383](https://github.com/facebook/react/pull/9383).
+* Envify and collapse create-react-class UMD. [See #9383](https://github.com/facebook/react/pull/9383).
+
+## CSS Transition Group & Transition Group
+
+## Linked State Mixin
+
+### 15.5.2
+
+* Envify and collapse LinkedStateMixin UMD. [See #9383](https://github.com/facebook/react/pull/9383).
+
+## Linked Input
+
+### 15.5.1
+
+* Remove unused prop-types dep. [See #9383](https://github.com/facebook/react/pull/9383).
+* Fix change handling. [See #9383](https://github.com/facebook/react/pull/9383).
+* Fix and collapse LinkedInput UMD. [See #9383](https://github.com/facebook/react/pull/9383).
+
+## Pure Render Mixin
+
+### 15.5.2
+* No significant changes
+
+## Shallow Compare
+
+### 15.5.2
+
+* Uninline shallowEqual in shallowCompare. [See #9385](https://github.com/facebook/react/pull/9385).
+
+## Test Utils
+
+### 15.5.1
+
+* No significant changes
+

CHANGELOG.md

@@ -1,3 +1,21 @@
+## 15.5.4 (April 11, 2017)
+
+* Fix compatibility with Enzyme by exposing `batchedUpdates` on shallow renderer. [See #9382](https://github.com/facebook/react/commit/69933e25c37cf5453a9ef132177241203ee8d2fd).
+* Updates to add-ons - [see add-ons changelog](https://github.com/facebook/react/blob/master/ADD-ONS-CHANGELOG.md).
+
+## 15.5.3 (April 7, 2017)
+
+* Updates to add-ons - [see add-ons changelog](https://github.com/facebook/react/blob/master/ADD-ONS-CHANGELOG.md).
+
+## 15.5.2 (April 7, 2017)
+
+* Updates to add-ons - [see add-ons changelog](https://github.com/facebook/react/blob/master/ADD-ONS-CHANGELOG.md).
+
+## 15.5.1 (April 7, 2017)
+
+* Fix erroneous PropTypes access warning ([see this commit](https://github.com/facebook/react/commit/ec97ebbe7f15b58ae2f1323df39d06f119873344))
+* Fix bug in `prop-types` - [see PropTypes changelog](https://github.com/reactjs/prop-types/blob/master/CHANGELOG.md).
+
 ## 15.5.0 (April 7, 2017)
 
 ### React