docs(developer): add docs for contributors

DEVELOPER.md

@@ -0,0 +1,22 @@
+## Unit Tests
+
+### Write Unit Tests
+
+Write tests alongside components and services, as `<thing>.spec.ts`:
+```
+components/
+ - About.ts
+ - About.spec.ts
+```
+
+### Run Tests with Karma
+```
+$ npm test
+```
+
+Or
+
+```
+$ npm install -g karma
+$ karma start
+```

package.json

@@ -4,7 +4,7 @@
   "description": "",
   "main": "index.js",
   "scripts": {
-    "test": "echo \"Error: no test specified\" && exit 1"
+    "test": "karma start"
   },
   "author": "",
   "license": "MIT",