add in stale bot (apollographql#816)

Author: James Baxley

.github/stale.yml

@@ -0,0 +1,15 @@
+# two weeks without any progress / comments mark issue as stale
+daysUntilStale: 14
+# one week after marked stale, close the issue
+daysUntilClose: 7
+# whitelist of lables to not mark stale
+exemptLables:
+  - pinned
+  - security
+  - enhancement
+# text of the comment when marking issue as stale
+markComment: >
+  This issue has been automatically marked as stale becuase it has not had recent activity. It will be closed if not further activity occurs. Thank you for your contributions to React Apollo!
+# text of the comment when closing an issue
+closeComment: >
+  This issue has been automatically closed because it has not had recent activity after being marked as stale. If you belive this issue is still a problem or should be reopened, please reopen it! Thank you fo ryour contributions to React Apollo!