Add descriptions to timestamp i18n strings

// FREEBIE

_locales/en/messages.json

@@ -310,43 +310,44 @@
         "description": "Informational text displayed if a sync operation times out."
     },
     "timestamp_s": {
-       "description": "",
+       "description": "Short or abbreviated timestamp for messages sent less than a minute ago. Displayed in the conversation list.",
        "message": "now"
     },
     "timestamp_m": {
-      "description": "",
+      "description": "Short or abbreviated timestamp for messages sent a minute ago. Displayed in the conversation list.",
       "message": "1 min"
     },
     "timestamp_mm": {
-       "description": "",
+        "description": "Short or abbreviated timestamp for messages sent multiple minutes ago. Displayed in the conversation list.",
        "message": "%d min"
     },
     "timestamp_h": {
-       "description": "",
+        "description": "Short or abbreviated timestamp for messages sent about an hour ago. Displayed in the conversation list.",
        "message": "1 hour"
     },
     "timestamp_hh": {
+        "description": "Short or abbreviated timestamp for messages sent multiple hours ago. Displayed in the conversation list.",
        "description": "",
        "message": "%d hours"
     },
     "extendedTimestamp_s": {
-       "description": "",
+        "description": "Timestamp for messages sent less than a minute ago. Displayed in the message bubble.",
        "message": "now"
     },
     "extendedTimestamp_m": {
-       "description": "",
+       "description": "Timestamp for messages sent about a minute ago. Displayed in the message bubble.",
        "message": "1 minute ago"
     },
     "extendedTimestamp_mm": {
-       "description": "",
+       "description": "Timestamp for messages sent multiple minutes ago. Displayed in the message bubble.",
        "message": "%d minutes ago"
     },
     "extendedTimestamp_h": {
-       "description": "",
+       "description": "Timestamp for messages sent one hour ago. Displayed in the message bubble.",
        "message": "1 hour ago"
     },
     "extendedTimestamp_hh": {
-       "description": "",
+       "description": "Timestamp for messages sent multiple hours ago. Displayed in the message bubble.",
        "message": "%d hours ago"
     }
 }