Adds reference to the new highlight-selected plugin

Author: abe33

Readme.md

@@ -42,6 +42,7 @@ The minimap can be augmented with plugins, belows the list of available plugins
   * [Find And Replace](https://atom.io/packages/minimap-find-and-replace)
   * [Git Diff](https://atom.io/packages/minimap-git-diff)
   * [Color Highlight](https://atom.io/packages/minimap-color-highlight)
+  * [Highlight Selected](https://atom.io/packages/minimap-highlight-selected)
 
 ### Roadmap