Add basic scheduler explanation

docs/user-manual/cron-basic-schedule.rst

@@ -0,0 +1,24 @@
+.. _cron_basic_schedule:
+
+CRON basic schedule
+===================
+
+The idea behind cron is to schedule tasks at specific interval or period of time.
+
+Library does not provide generic scheduler that would do that automatically for you,
+instead user should manually implement custom scheduler to periodically check and schedule should cron execute or not.
+
+.. tip::
+    A check should be performed at least at minimum cron granularity, that being ``1 second`` in the current revision.
+
+Basic example is very simple and does the following:
+
+* Parses cron defined by user with :cpp:`lwdtc_cron_parse` function
+* Reads system time periodically (example was tested under *Windows* environment)
+* It checks if cron is valid for execution each time new time changes versus previous check
+* It executes task
+
+.. literalinclude:: ../../examples/cron_basic.c
+    :language: c
+    :linenos:
+    :caption: Basic CRON example with parser

docs/user-manual/index.rst

@@ -7,4 +7,5 @@ User manual
     :maxdepth: 2
 
     cron
+    cron-basic-schedule
     cron-dt-range