Add probot-stale configuration (#982)

.github/stale.yml

@@ -0,0 +1,21 @@
+# Configuration for probot-stale - https://github.com/probot/stale
+
+# Number of days of inactivity before an issue becomes stale
+daysUntilStale: 60
+# Number of days of inactivity before a stale issue is closed
+daysUntilClose: 7
+# Issues with these labels will never be considered stale
+exemptLabels:
+  - 'status: blocked'
+  - 'status: help wanted'
+  - 'status: in-progress'
+  - 'status: on hold'
+# 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 in 7 days if no further activity occurs. 
+  Thank you for your contributions.
+# Comment to post when closing a stale issue. Set to `false` to disable
+closeComment: false