chore(package): Add TestPilot link in package description

chore(package): Add newline to package.json description

package.json

@@ -1,6 +1,6 @@
 {
   "name": "activity-streams",
-  "description": "A rich visual history feed and a reimagined home page make it easier than ever to find exactly what you're looking for in Firefox.",
+  "description": "A rich visual history feed and a reimagined home page make it easier than ever to find exactly what you're looking for in Firefox.\n\nLearn more about this Test Pilot experiment at https://testpilot.firefox.com/.",
   "version": "1.0.14",
   "author": "Mozilla (https://mozilla.org/)",
   "bugs": {