Update metadata

Author: wooorm

package.json

@@ -1,13 +1,17 @@
 {
   "name": "nlcst-to-string",
   "version": "2.0.3",
-  "description": "Stringify NLCST",
+  "description": "nlcst utility to transform a tree to a string",
   "license": "MIT",
   "keywords": [
+    "unist",
     "nlcst",
-    "retext",
-    "to",
-    "string"
+    "nlcst-util",
+    "util",
+    "utility",
+    "string",
+    "serialize",
+    "stringify"
   ],
   "repository": "syntax-tree/nlcst-to-string",
   "bugs": "https://github.com/syntax-tree/nlcst-to-string/issues",