Added stale bot (#370)

* added stale bot

* added stale bot

* added stale bot

.github/stale.yml

@@ -0,0 +1,27 @@
+# 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.
+# Set to false to disable. If disabled, issues still need to be closed manually, but will remain marked as stale.
+daysUntilClose: 7
+
+# Issues with these labels will never be considered stale. Set to `[]` to disable
+exemptLabels:
+  - bug
+  - docs improvement
+  - help wanted
+
+# Label to use when marking as stale
+staleLabel: stale
+
+issues:
+  # Comment to post when marking Issues as stale.
+  markComment: >
+    This issue has been automatically marked as stale because it has not had any
+    recent activity. It will be closed in 7 days if no further activity occurs.
+  # Comment to post when closing a stale Issue.
+  closeComment: >
+    This issue has been automatically closed because it has not had any recent
+    activity. If you have a question or comment, please open a new issue.