update readme regarding node.js versions

Author: jeffbski

README.md

@@ -12,7 +12,8 @@ wait-on can also be used in reverse mode which waits for resources to NOT be ava
 
 ## Installation
 
-Latest version 4+ requires Node.js 10+
+Latest wait-on version 7+ requires Node.js 12+
+wait-on versions 4-6 requires Node.js 10+
 
 (Node.js v8 users can use [email protected], v4 users can still use [email protected], and older Node.js
 engines, use [email protected])