Add server rules (#15769)

config/locales/simple_form.en.yml

@@ -73,6 +73,8 @@ en:
           no_access: Block access to all resources
           sign_up_requires_approval: New sign-ups will require your approval
         severity: Choose what will happen with requests from this IP
+      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:'
         webauthn: If it's an USB key be sure to insert it and, if necessary, tap it.
@@ -197,6 +199,8 @@ en:
         reblog: Someone boosted your status
         report: New report is submitted
         trending_tag: An unreviewed hashtag is trending
+      rule:
+        text: Rule
       tag:
         listable: Allow this hashtag to appear in searches and on the profile directory
         name: Hashtag