fix #15: add stalebot config

Author: kamilsk

.github/stale.yml

@@ -0,0 +1,16 @@
+daysUntilStale: 60
+daysUntilClose: 7
+
+exemptLabels: [ 'status: pending' ]
+exemptProjects: true
+exemptMilestones: true
+exemptAssignees: true
+
+staleLabel: 'status: stale'
+
+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. Thank you
+  for your contributions.
+
+closeComment: false