doc: wifi: Improve runtime cert docs

* Remove the obsolete path reference, command is enough
* Add a note for the volatility of the certificates

Signed-off-by: Chaitanya Tata <[email protected]>

Author: krish2718

doc/connectivity/networking/api/wifi.rst

@@ -73,7 +73,7 @@ Run time certificates
 The Wi-Fi shell module uses TLS credentials subsystem to store and manage the certificates. The certificates can be added at runtime using the shell commands, see :ref:`tls_credentials_shell` for more details.
 The sample or application need to enable the :kconfig:option:`CONFIG_WIFI_SHELL_RUNTIME_CERTIFICATES` option to use this feature.
 
-To facilitate installation of the certificates, a helper script is provided in the ``samples/net/wifi/test_certs`` directory. The script can be used to install the certificates at runtime.
+To facilitate installation of the certificates, a helper script is provided, see below for usage.
 
 .. code-block:: bash
 
@@ -96,6 +96,10 @@ Any AAA server can be used for testing purposes, for example, ``FreeRADIUS`` or
     The certificates are for testing purposes only and should not be used in production.
     They are generated using `FreeRADIUS raddb <https://github.com/FreeRADIUS/freeradius-server/tree/master/raddb/certs>`_ scripts.
 
+.. note::
+
+    When using TLS credentials subsystem, by default the volatile backend i.e., :kconfig:option:`CONFIG_TLS_CREDENTIALS_BACKEND_VOLATILE` is chosen. When using the volatile backend, the certificates are stored in RAM and are lost on reboot, so the certificates need to be installed again after reboot. As an alternative, the PS (protected storage) backend i.e., :kconfig:option:`CONFIG_TLS_CREDENTIALS_BACKEND_PROTECTED_STORAGE` can be used to store the certificates in the non-volatile storage.
+
 API Reference
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