Move English documentation to folder en_US

doc/en_US/cronjob.markdown

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+Background Job Scheduling
+=========================
+
+To work properly, Kanboard requires that a background job run on a daily basis.
+Usually on Unix platforms, this process is done by `cron`.
+
+This background job is necessary for these features:
+
+- Reports and analytics (calculate daily stats of each projects)
+- Send overdue task notifications
+- Execute automatic actions connected to the event "Daily background job for tasks"
+
+Configuration on Unix and Linux platforms
+-----------------------------------------
+
+There are multiple ways to define a cronjob on Unix/Linux operating systems, this example is for Ubuntu 14.04.
+The procedure is similar for other systems.
+
+Edit the crontab of your web server user:
+
+```bash
+sudo crontab -u www-data -e
+```
+
+Example to execute the daily cronjob at 8am:
+
+```bash
+0 8 * * * cd /path/to/kanboard && ./cli cronjob >/dev/null 2>&1
+```
+
+Note: the cronjob process must have write access to the database in case you are using Sqlite.
+Usually, running the cronjob under the web server user is enough.
+
+Configuration on Microsoft Windows Server
+-----------------------------------------
+
+Before to configure the recurring task, create a batch file (*.bat or *.cmd) that run the Kanboard CLI script.
+
+Here an example (`C:\kanboard.bat`):
+
+```
+"C:\php\php.exe" -f "C:\inetpub\wwwroot\kanboard\kanboard" cronjob
+```
+
+**You must change the path of the PHP executable and the path of the Kanboard's script according to your installation.**
+
+Configure the Windows Task Scheduler:
+
+1. Go to "Administrative Tools"
+2. Open the "Task Scheduler"
+3. On the right, choose "Create Task"
+4. Choose a name, for example you can use "Kanboard"
+5. Under "Security Options", choose a user that can write to the database in case you are using Sqlite (might be IIS_IUSRS depending of your configuration)
+6. Create a new "Trigger", choose daily and a time, midnight for example
+7. Add a new action, choose "Start a program" and select the batch file created above