Add note about manufacturing db dependency

README.adoc

@@ -165,6 +165,8 @@ Set to any value to enable EEPROM write protection.
 === RPI_SB_PROVISONER_MANUFACTURING_DB
 *Optional*
 
+NOTE: This option only has effect when you also use RPI_DEVICE_FETCH_METADATA. If that flag is not set, no manufacturing data will be collected.
+
 Store manufacturing data in a sqlite3 database. This will include the board serial, board revision, the boot ROM version, the MAC address of the ethernet port, any set hash of the customer signing key, the JTAG lock state, the board attributes and the advanced boot flags.
 
 You must not specify the path of a database stored on a network drive or similar storage, as this mechanism is only safe to use on a single provisioning system. For merging the output with multiple provisioning systems, consider "Processing the manufacturing database" later in this document.