Add CONTRIBUTING.md - general instruction for contributors

CONTRIBUTING.md

@@ -0,0 +1,7 @@
+# UAParser.js: How to Contribute
+
+* Fork and clone this repository
+* Make some changes as required
+* Write unit test to showcase its functionality under `/test`
+* Run the test suites to make sure it's not breaking anything `$ npm run build+test`
+* Submit a pull request under `develop` branch & check the CLA in the submission form

package.json

@@ -190,6 +190,7 @@
   ],
   "scripts": {
     "build": "./script/build-dist.sh && ./script/build-module.js",
+    "build+test": "npm run build && npm run test",
     "fuzz": "jazzer ./test/jazzer-fuzz-test.js --sync",
     "test": "./script/test-all.sh",
     "test:eslint": "eslint src && eslint script",