Add basic scheduler docs

docs/source/index.rst

@@ -10,6 +10,8 @@ Welcome to redis-tasks's documentation!
    :maxdepth: 2
    :caption: Contents:
 
+   scheduler
+
 
 
 Indices and tables

docs/source/scheduler.rst

@@ -0,0 +1,43 @@
+Scheduler
+=========
+
+``redis-tasks`` provides developers with an built-in task scheduler.
+A schedule is defined as a setting ``RT_SCHEDULE``, which is a dict of the
+structure ``id`` -> ``entry``. An ``entry`` itself is a dict with the
+following keys:
+
+- ``task``: Import path of the function to be run, e.g. ``mymodule.myfunc``
+- ``schedule``: Schedule for this task (see below)
+- ``args``: args for the task function (optional)
+- ``kwargs``: kwargs for the task function (optional)
+- ``singleton``: Boolean to specify whether this task should not be on the queue
+    multiple times (optional, defaults to ``True``)
+- ``queue``: Queue to put this task on (optional, defaults to
+    ``RT_SCHEDULER_QUEUE``)
+
+``schedule`` for a task can be represented in multiple ways:
+
+1. as a crontab, for example to run a task every Monday you would set::
+
+    "schedule": redis_tasks.crontab("0 0 * * 1")
+
+2. as a periodic schedule defined with ``redis_tasks.run_every()``, which
+    accepts the following keyword-only arguments:
+
+    - ``hours``
+    - ``minutes``
+    - ``seconds``
+    - ``start_at``: a string in the format <hours>:<minutes>
+
+    For example if you want your task run every 6 hours starting at 5:00 every
+    day, you would set::
+
+        "schedule": redis_tasks.run_every(hours=6, start_at="05:00")
+
+    This would run a task at 5:00, 11:00 , 17:00, 23:00.
+3. as a daily task defined with ``redis_tasks.once_per_day()``, which accepts a
+    single string argument in the format <hours>:<minutes>.
+    For example to run a task every day at 12:00, you would set::
+
+        "schedule": redis_tasks.once_per_day("12:00")
+