Add Stacks by Stack Overflow (#142)

Closes #97.

Author: wooky

readme.md

@@ -177,6 +177,12 @@ Frameworks that are smaller than ~5KB.
   [Repo](https://github.com/patternfly/patternfly)
   | #SCSS #LESS
 
+- [**Stacks**](https://stackoverflow.design/) - UI components used by Stack Overflow.  
+  ![](https://img.shields.io/github/stars/StackExchange/Stacks.svg?style=social&label=Star)
+  [Docs](https://stackoverflow.design/product/develop/using-stacks/),
+  [Repo](https://github.com/StackExchange/Stacks)
+  | #LESS
+
 - [**HiQ**](https://jonathanharrell.github.io/hiq/) - Simple CSS foundation with responsive typography and input styling.  
   ![](https://img.shields.io/github/stars/jonathanharrell/hiq.svg?style=social&label=Star)
   [Docs](https://jonathanharrell.github.io/hiq/guide/),