Actually write README

README.md

@@ -3,6 +3,33 @@
 Zendesk Time Tracking app
 ===============
 
-This is the [Time Tracking app](https://support.zendesk.com/entries/70306826) for New Zendesk. 
+From the [Help Center article](https://support.zendesk.com/hc/en-us/articles/203691196-Using-the-Time-Tracking-app-Plus-and-Enterprise-):
 
-Pull requests are welcome
+>    “The Time Tracking app enables you to monitor how much time you spend on tickets.”
+
+It looks like this:
+
+![Timetracking App main interface](http://zen-marketing-documentation.s3.amazonaws.com/docs/en/time-tracking-timer-controls.png)
+
+It also allows admins (and optionally agents) to review the logs:
+
+![TT app review screen](http://zen-marketing-documentation.s3.amazonaws.com/docs/en/time-tracking-timelogs.png)
+
+It also lets people edit their “time spent” before they submit a ticket.
+
+There are a whole bunch of settings, which are [documented in Help Center](https://support.zendesk.com/hc/en-us/articles/203662506-Setting-up-the-Time-Tracking-app-Plus-and-Enterprise-):
+
+![TT settings](https://www.evernote.com/shard/s162/sh/a5cd5e63-34cb-4197-a9af-9bb76de727f9/bfc6b57fe98b5e6b6f09588f00e2d4f1/deep/0/a_-_Agent.png)
+
+## Implementation
+
+From a [Help Center article about setting up the app](https://support.zendesk.com/hc/en-us/articles/203662506-Setting-up-the-Time-Tracking-app-Plus-and-Enterprise-#topic_vdh_vs2_44):
+
+>   “When you install Time Tracking, it automatically creates two custom ticket fields, Time spent since last update and Total time spent.”
+
+When the ticket is submitted, the time tracking app sets the “time spent since last update” field to whatever has been timed by the app, and then sets the “total time spent” field to the previous value of that field plus the “time spent since last update” field.
+
+
+## Contributing
+
+Pull requests and bug reports are very welcome :heart: