zephyr: Update documents with CBI FW_CONFIG feature
Add the CBI FW_CONFIG feature to the documentation.
TEST=none
BRANCH=none
@@ -59,6 +59,7 @@ EC Feature | Ne
[Configure GPIO](./zephyr_gpio.md) | yes
[Configure Batteries (TODO)](./zephyr_template.md) | no
[Configure CrOS Board Information (CBI) (TODO)](./zephyr_template.md) | no
+[Configure CrOS CBI FW CONFIG](./zephyr_fw_config.md) | no
[Configure Keyboard (TODO)](./zephyr_template.md) | no
[Configure LEDs (TODO)](./zephyr_template.md) | no
[Configure Motion Sensors (TODO)](./zephyr_template.md) | no
