ec/google/wilco: Extend description of `EC_GOOGLE_WILCO`

Change-Id: Ia278b538a8904651d16c37d095972fa78e264288
Link: https://mail.coreboot.org/hyperkitty/list/coreboot@coreboot.org/thread/7S5OJMLQUEIU6YK36JTTRINF5OOCI66V/
Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/54929
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
diff --git a/src/ec/google/wilco/Kconfig b/src/ec/google/wilco/Kconfig
index ee7b556..f97fa26d 100644
--- a/src/ec/google/wilco/Kconfig
+++ b/src/ec/google/wilco/Kconfig
@@ -7,6 +7,13 @@
 	help
 	  Google Wilco Embedded Controller interface.
 
+	  Note, the Wilco EC firmware is a modified version of Dell's
+	  typical Latitude EC firmware, that implements a custom mailbox
+	  protocol similar to the one used in the Chromium EC.
+
+	  This particular EC firmware is not open source, just the
+	  host-side interfaces (kernel and firmware drivers) are.
+
 if EC_GOOGLE_WILCO
 
 config EC_BASE_ACPI_DATA