Add description to example mod (#2)

src/main/resources/fabric.mod.json

 {
   "id": "modid",
   "name": "Example Mod",
+  "description": "This is an example description! Tell everyone what your mod is about!",
   "version": "1.0.0",
   "side": "universal",
   "initializer": "net.fabricmc.example.ExampleMod",