Add stale config

.github/stale.yml

@@ -0,0 +1,21 @@
+# Number of days of inactivity before an issue becomes stale
+daysUntilStale: 120
+# Number of days of inactivity before a stale issue is closed
+daysUntilClose: 30
+# Issues with these labels will never be considered stale
+exemptLabels:
+  - Keep
+  - Security
+# Label to use when marking an issue as stale
+staleLabel: Stale
+# Comment to post when marking an issue as stale. Set to `false` to disable
+markComment: >
+  This issue has been automatically marked as stale because it has not had
+  recent activity. The resources of the Hugo team are limited, and so we are asking for your help.
+
+  If you still think this is important, please tell us why.
+
+  This issue will automatically be closed in the near future if no further activity occurs. Thank you for all your contributions.
+  
+# Comment to post when closing a stale issue. Set to `false` to disable
+closeComment: false