Add hints for rules (#29539)

config/locales/simple_form.en.yml

@@ -116,6 +116,7 @@ en:
           sign_up_requires_approval: New sign-ups will require your approval
         severity: Choose what will happen with requests from this IP
       rule:
+        hint: Optional. Provide more details about the rule
         text: Describe a rule or requirement for users on this server. Try to keep it short and simple
       sessions:
         otp: 'Enter the two-factor code generated by your phone app or use one of your recovery codes:'
@@ -299,6 +300,7 @@ en:
           patch: Notify on bugfix updates
         trending_tag: New trend requires review
       rule:
+        hint: Additional information
         text: Rule
       settings:
         indexable: Include profile page in search engines