Update docs/source/carrierboard_development.rst

Co-authored-by: barsnick <barsnick@users.noreply.github.com>

Author: mhei

docs/source/carrierboard_development.rst

@@ -129,7 +129,7 @@ Such a signature can be created for example using the following command line:
 It is possible to re-use an existing Public-Key Infrastructure which is already used for signing the firmware
 update files.
 
-Once a matching Device Tree overlay and the corresponding signature is available, the EEPROM content needs to be created
+Once a matching Device Tree overlay and the corresponding signature are available, the EEPROM content needs to be created
 using the helper tool ``cb-dt-eeprom`` which is included in
 chargebyte's Github space: https://github.com/chargebyte/cb-eeprom-utils