samples: charger: Adds additional context to README

Adds useful context to the charger sample README to help readers
understand what the sample application is doing.

Signed-off-by: Ricardo Rivera-Matos <ricardo.rivera-matos@cirrus.com>

Author: rriveramcrus

samples/drivers/charger/README.rst

@@ -7,4 +7,18 @@
 Overview
 ********
 
-This sample demonstrates how to use the :ref:`charger_api`.
+This sample demonstrates how to use the :ref:`charger_api` API.
+
+The sample application performs a simple charging task loop.
+
+- The application will first poll for external power provided to the charger device.
+- If power is provided to the charger, then the sample application will attempt to enable the charge
+  cycle.
+- After the charge cycle is initiated, the sample application will check the status property of the
+  charger device and report any relevant information to the log.
+- Once the charger device reports that the charge cycle has completed, the application returns.
+
+Note that this sample terminates once the charge cycle completes and does not attempt to "top-off"
+the battery pack. Additionally, the sample intentionally does not respond to the reported charger
+health state and the implications the environment may have on the charge cycle execution. The
+responsibility of responding to these events falls on the user or the charger device implementation.