update target requirements

docs/development/manufacturer/requirements-for-submission-of-targets.md

@@ -9,3 +9,5 @@ The following new requirements for pull requests adding new targets or modifying
 3. For any new targets, a definition file needs to be submitted to https://github.com/betaflight/config. See the [instructions](https://betaflight.com/docs/development/manufacturer/creating-configuration) for how to create a configuration file.
 
 4. For changes to existing targets, consider updating both https://github.com/betaflight/config and https://github.com/betaflight/unified-targets.
+
+5. Upon approval and merging, consider adding [board documentation](https://betaflight.com/docs/category/boards) as per [documentation guidelines](https://betaflight.com/docs/development/manufacturer/fc_documentation/how-to-create-board-documentation).