Include documentation in the application

doc/time-tracking.markdown

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+Time Tracking
+=============
+
+Time tracking information can be defined at the task level or at the subtask level.
+
+Task time tracking
+------------------
+
+![Task time tracking](http://kanboard.net/screenshots/documentation/task-time-tracking.png)
+
+Tasks have two fields:
+
+- Time estimated
+- Time spent
+
+These values represents hours of work and have to be set manually.
+
+Subtask time tracking
+---------------------
+
+![Subtask time tracking](http://kanboard.net/screenshots/documentation/subtask-time-tracking.png)
+
+Subtasks also have the fields "time spent" and "time estimated".
+
+When you change the value of these fields, **the task time tracking values are updated automatically and becomes the sum of all subtask values**.
+
+Kanboard records the time between each subtask status change in a separate table.
+
+- Changing subtask status from **todo** to **in pogress** logs the start time
+- Changing subtask status from **in progress** to **done** logs the end time but also update the time spent of the subtask and the task
+
+The breakdown of all records is visible in the task view page:
+
+![Task timesheet](http://kanboard.net/screenshots/documentation/task-timesheet.png)
+
+For each subtask, the timer can be stopped/started at any time:
+
+![Subtask timer](http://kanboard.net/screenshots/documentation/subtask-timer.png)
+
+- The timer doesn't depends of the subtask status
+- Each time you start the timer a new record is created in the time tracking table
+- Each time you stop the clock the end date is recorded in the time tracking table
+- The calculated time spent is rounded to the nearest quarter