add js package skeleton

js/pmtiles.js

@@ -0,0 +1,11 @@
+(function (root, factory) {
+    if (typeof define === 'function' && define.amd) {
+        define([], factory);
+    } else if (typeof module === 'object' && module.exports) {
+        module.exports = factory();
+    } else {
+        root.pmtiles = factory();
+  }
+}(typeof self !== 'undefined' ? self : this, function () {
+    return {pmtiles:true};
+}));