Create stale.yml

Adding stale.yml file for nagging bot.

BUG=improving github process.

.github/stale.yml

+# Number of days of inactivity before an Issue or Pull Request becomes stale
+daysUntilStale: 30
+# Number of days of inactivity before a stale Issue or Pull Request is closed
+daysUntilClose: 15
+# Only issues or pull requests with all of these labels are checked if stale. Defaults to `[]` (disabled)
+onlyLabels:
+ - stat:awaiting response
+# Comment to post when marking as stale. Set to `false` to disable
+markComment: >
+  This issue has been automatically marked as stale because it has no
+  recent activity. It will be closed if no further activity occurs. Thank you.
+# Comment to post when removing the stale label. Set to `false` to disable
+unmarkComment: false
+closeComment: >
+  Closing as stale. Please reopen if you'd like to work on this further.
+limitPerRun: 30
+# Limit to only `issues` or `pulls`
+only: issues