Added legacy release comment

Author: gmsa

README.md

@@ -35,6 +35,7 @@ vue-grid-layout is a grid layout system, like [Gridster](http://dsmorse.github.i
 
 ## **Current version:** 2.3.12 (Supports Vue 2.2+)
 
+#### **For legacy browsers**, like IE11, use version [2.3.12-legacy](https://github.com/jbaysolutions/vue-grid-layout/tree/legacy)
 #### **For Vue 2.1.10 and below use version [2.1.3](https://github.com/jbaysolutions/vue-grid-layout/tree/2.1.3)**
 #### **For Vue 1 use version [1.0.3](https://github.com/jbaysolutions/vue-grid-layout/tree/1.0.3)**