implements a stale issues policy, fixes #212

.github/stale.yml

@@ -0,0 +1,17 @@
+# Number of days of inactivity before an issue becomes stale
+daysUntilStale: 180
+# Number of days of inactivity before a stale issue is closed
+daysUntilClose: 7
+# Issues with these labels will never be considered stale
+exemptLabels:
+  - pinned
+  - security
+# 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 if no further activity occurs. If it should not be closed, please comment! Thank you
+  for your contributions.
+# Comment to post when closing a stale issue. Set to `false` to disable
+closeComment: false

guidelines/project_guidelines.md

@@ -82,3 +82,8 @@ See the [`LICENSE`](/LICENSE) file for details.
  * FITNESS FOR A PARTICULAR PURPOSE. See LICENSE file for details.
  */
 ```
+
+## Stale Issues Policy
+In order to keep issues up to date, we use [a bot](https://probot.github.io/apps/stale/) to mark issues stale after a period of time with no activity, comment, and then close the issue if there is still no new activity.
+
+To see the configuration (number of days until stale, number of days until the issue is closed), see this repo's `.github/stale.yml`.