Add keywords field to package.json

Author: ragona

package.json

@@ -3,6 +3,7 @@
   "private": true,
   "version": "0.0.1",
   "description": "AWS Encryption SDK for JavaScript",
+  "keywords": ["cryptography", "crypto", "encryption", "envelope encryption", "client side encryption", "CSE", "aws"],
   "main": "index.js",
   "scripts": {
     "bootstrap": "./util/bootstrap_tsconfig && lerna bootstrap",