Add stale.yml

To help manage old issues that have been inactive for a year or more.

https://probot.github.io/apps/stale/

.github/stale.yml

@@ -0,0 +1,13 @@
+# Number of days of inactivity before an issue becomes stale
+daysUntilStale: 360
+# Number of days of inactivity before a stale issue is closed
+daysUntilClose: 7
+# Issues with these labels will never be considered stale
+exemptLabels:
+# 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. It will be closed if no further activity occurs.
+# Comment to post when closing a stale issue. Set to `false` to disable
+closeComment: false