docs(card10.cfg): Add config option for flashlight LED

Add a config option to indicate that a flashlight LED was soldered onto
the harmonic board.

Documentation/card10-cfg.rst

@@ -64,4 +64,6 @@ Option name        Type       Description
 ``bsec_offset``    Integer    Temperature offset in .1 K. Example: Set to `-14` if temperature reads 1.4 "C" to high. Default: -2.2 K (appropriate for a card10 without a case, connected to USB and with BLE active in vertical orientation).
 ------------------ ---------- -----------
 ``battery_check``  Boolean    Whether the low battery check should be enabled (default ``true``).  **Warning**: Do not use this unless you know what you're doing.  This option is only meant to be used on devices with a broken PMIC ADMUX connection.
+------------------ ---------- -----------
+``has_flashlight`` Boolean    Whether the flashlight LED was soldered onto the harmonic board.  Can be used by apps to optionally enable flashlight features.
 ================== ========== ===========