Describe NodeJS limitation

README.md

@@ -20,6 +20,8 @@ We wanted to be able to write Javascript that used crypto on both the client and
 
 **At this time this solution should be considered suitable for research and experimentation, further code and security review is needed before utilization in a production application.**
 
+**Module is based on NodeJS v10 Crypto API. It would work only with Node v10 and higher.**
+
 ## Installing
 
 ```

package.json

@@ -75,5 +75,8 @@
       "text-summary",
       "html"
     ]
+  },
+  "engines": {
+    "node": ">=10.0.0"
   }
 }