Merge pull request #32159 from bogdanvlviv/5-2-stable-update-guide-changelog-file

Update `guides/CHANGELOG.md`

guides/CHANGELOG.md

 ## Rails 5.2.0.rc1 (January 30, 2018) ##
 
-*   No changes.
+*   Add "Active Storage Overview" Guide.
+
+    *Jeffrey Guenther*, *George Claghorn*
 
 
 ## Rails 5.2.0.beta2 (November 28, 2017) ##
@@ -10,6 +12,9 @@
 
 ## Rails 5.2.0.beta1 (November 27, 2017) ##
 
-*   No changes.
+*   Add "Threading and Code Execution in Rails" Guide.
+
+    *Matthew Draper*
+
 
 Please check [5-1-stable](https://github.com/rails/rails/blob/5-1-stable/guides/CHANGELOG.md) for previous changes.