samples/subsys/settings: add the readme doc

Added readme file for the sample

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>

doc/reference/runtime_conf/index.rst

@@ -15,6 +15,9 @@ storage medium, and even change it later as needs change.
 The runtime configuration system is used by various Zephyr
 components and can be used simultaneously by user applications.
 
+For an example of the settings module refer to
+:ref:`the sample <settings_subsys_sample>`.
+
 .. toctree::
    :maxdepth: 1
 

samples/subsys/settings/README.rst

@@ -0,0 +1,100 @@
+.. _settings_subsys_sample:
+
+Settings sample
+###############
+
+Overview
+********
+
+This is a simple application demonstrating use of the settings runtime
+configuration module. In this application some configuration values are loaded
+form persistient storage and exported to persistent storage using different
+settings method. The example shows how to implement module handlers, how to
+register them.
+
+Requirements
+************
+
+* A board with settings support, for instance: nrf52840_pca10056
+* Or qemu_x86 target
+
+Building and Running
+********************
+
+This sample can be found under :zephyr_file:`samples/subsys/settings` in
+the Zephyr tree.
+
+The sample can be build for several platforms, the following commands build the
+application for the qemu_x86.
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/subsys/settings
+   :board: qemu_x86
+   :goals: build flash
+   :compact:
+
+After running the image to the board the output on the console shows the
+settings manipulation messages.
+
+Sample Output
+=============
+
+.. code-block:: console
+
+   ***** Booting Zephyr OS build v2.1.0-rc1-123-g41091eb1d5e0 *****
+
+   *** Settings usage example ***
+
+   settings subsys initialization: OK.
+   subtree <alpha> handler registered: OK
+   subtree <alpha/beta> has static handler
+
+   ##############
+   # iteration 0
+   ##############
+
+   =================================================
+   basic load and save using registered handlers
+
+   load all key-value pairs using registered handlers
+   loading all settings under <beta> handler is done
+   loading all settings under <alpha> handler is done
+
+   save <alpha/beta/voltage> key directly: OK.
+
+   load <alpha/beta> key-value pairs using registered handlers
+   <alpha/beta/voltage> = -3025
+   loading all settings under <beta> handler is done
+
+   save all key-value pairs using registered handlers
+   export keys under <beta> handler
+   export keys under <alpha> handler
+
+   load all key-value pairs using registered handlers
+   export keys under <beta> handler
+   export keys under <alpha> handler
+
+   =================================================
+   loading subtree to destination provided by the caller
+
+   direct load: <alpha/length/2>
+   direct load: <alpha/length/1>
+   direct load: <alpha/length>
+     direct.length = 100
+     direct.length_1 = 41
+     direct.length_2 = 59
+
+   =================================================
+   Delete a key-value pair
+
+   immediate load: OK.
+     <alpha/length> value exist in the storage
+   delete <alpha/length>: OK.
+     Can't to load the <alpha/length> value as expected
+
+   =================================================
+   Service a key-value pair without dedicated handlers
+
+   <gamma> = 0 (default)
+   save <gamma> key directly: OK.
+   ...