Add npm publish configuration

Author: adamgraham

.npmrc

@@ -0,0 +1,3 @@
+registry=https://registry.npmjs.org/
+@zigurous:registry=https://npm.pkg.github.com
+//npm.pkg.github.com/:_authToken=

package.json

@@ -4,6 +4,10 @@
   "displayName": "Zigurous Animation Tweening",
   "description": "An animation system for tweening object properties in Unity.",
   "unity": "2019.4",
+  "repository": "https://github.com/zigurous/unity-animation-tweening",
+  "publishConfig": {
+    "registry": "https://npm.pkg.github.com/@zigurous"
+  },
   "author": {
     "name": "Zigurous",
     "email": "support@zigurous.com",