Documentation: firmware: Clarify firmware path usage

Newline characters will be taken into account for the firmware search
path parameter, warn users about that and provide an example using 'echo
-n' such that it clarifies the typical use of that parameter.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20230402135423.3235-1-f.fainelli@gmail.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/driver-api/firmware/fw_search_path.rst

@@ -22,5 +22,10 @@ can use the file:
 
 * /sys/module/firmware_class/parameters/path
 
-You would echo into it your custom path and firmware requested will be
-searched for there first.
+You would echo into it your custom path and firmware requested will be searched
+for there first. Be aware that newline characters will be taken into account
+and may not produce the intended effects. For instance you might want to use:
+
+echo -n /path/to/script > /sys/module/firmware_class/parameters/path
+
+to ensure that your script is being used.