Added call to donate after npm install (optional)

package.json

@@ -10,7 +10,8 @@
   "author": "Michelle Bu, Eric Zhang",
   "license": "MIT",
   "scripts": {
-    "prepublish": "./node_modules/.bin/grunt"
+    "prepublish": "./node_modules/.bin/grunt",
+    "postinstall": "opencollective-postinstall"
   },
   "devDependencies": {
     "expect.js": "*",
@@ -25,6 +26,11 @@
     "@types/webrtc": "0.0.21",
     "eventemitter3": "^0.1.5",
     "js-binarypack": "0.0.9",
+    "opencollective": "^1.0.3",
     "reliable": "git+https://github.com/michelle/reliable.git"
+  },
+  "collective": {
+    "type": "opencollective",
+    "url": "https://opencollective.com/peer"
   }
-}
+}