Add notification strings.

en.json

@@ -170,6 +170,10 @@
         "nextWeek": "dddd [at] LT",
         "sameElse": "L"
     },
+    "notifications": {
+        "sent_request": "@{{person}} sent you a friend request.",
+        "now_friends": "You are now friends with @{{person}}!"
+    },
     "error": {
         "unlabelled": "Something happened.",
         "failed_validation": "Failed to validate fields.",