Added Collaboration category

Added CodeSideStory to collaboration.

README.md

@@ -10,6 +10,8 @@ A curated list of delightful Atom packages and resources. For more awesomeness,
 - [Extensions](#extensions)
  - [Nuclide](#nuclide)
 - [Themes](http:https://enrmarc.github.io/atom-theme-gallery/)
+- [Collaboration](#collaboration)
+ - [CodeSideStory](#codesidestory)
 - [Uncategorized](#uncategorized)
  - [Nuclide](#nuclide)
  - [Advanced Open File](#advanced-open-file)
@@ -98,6 +100,13 @@ To enable building, you'll need the general [build](https://atom.io/packages/bui
 
 ![](https://nuclide.io/static/images/docs/promo-hack.png)
 
+## Collaboration
+
+#### [CodeSideStory](https://atom.io/packages/codesidestory-atom)
+> An Atom/Slack integration to start conversations about code right from the editor. Record screens and archive it right next to the line number to provide more context to your code.
+
+![](https://storage.googleapis.com/codesidestory/static/media/atom_ss.c29b4b0b.png)
+
 ## Uncategorized
 
 #### [Advanced Open File](https://atom.io/packages/advanced-open-file)