Clarify GRP for non-MISRA standards

Author: rvermeulen

docs/design/guideline_recategorization.md

@@ -174,4 +174,6 @@ A new SARIF file is created by applying the JSON Patch to the processed SARIF fi
 ## Non-MISRA standards
 
 Guideline recategorization applies to rules adhering to the MISRA categorizations.
-For standards that deviate from these conventions we assume that the rules have an *effective category* equivalent to MISRA’s *required* category.
+For standards that deviate from these conventions the rules have an *effective category* equivalent to MISRA’s *required* category.
+
+CERT rules, for example, are handled in the same way as MISRA's rules recategorized to *required*.