[RFC 0051] Mark stale nixpkgs issues (#51)

* rfc51: close stale issues initial draft

* rfc0051: use staleLabel consistent with nixpkgs labeling conventions

* rfc0051: do not close issues

* rfc0051: reword motivation

* record the members of the shepherd team

* Update rfcs/0051-mark-stale-issues.md

Co-Authored-By: asymmetric <lorenzo@mailbox.org>

* [RFC 0051] remove references to "issue" in stale message

rfcs/0051-mark-stale-issues.md

@@ -0,0 +1,83 @@
+---
+feature: mark-stale-issues
+start-date: 2019-08-24
+author: Ryan Mulligan
+co-authors: (find a buddy later to help our with the RFC)
+shepherd-team: @globin, @grahamc, and @peti
+shepherd-leader: @peti
+related-issues: (will contain links to implementation PRs)
+---
+
+# Summary
+[summary]: #summary
+
+Mark stale Nixpkgs issues and pull requests (hereafter both referred
+to as simply "issues") on GitHub using an application provided by
+GitHub.
+
+# Motivation
+[motivation]: #motivation
+
+We have a large number of open issues that have accumulated
+over the years. Not all of them are still valid and need our
+attention.
+
+By marking stale issues, we can more easily filter issues for ones
+that have at least one person interested in them.
+
+# Detailed design
+[design]: #detailed-design
+
+1. Use the [Stale](https://github.com/marketplace/stale) application
+   provided by GitHub on the [Nixpkgs
+   repository](https://github.com/NixOS/nixpkgs).
+2. Start by using the following `.github/stale.yml` configuration
+   file:
+
+   ```
+   # Number of days of inactivity before an issue becomes stale
+   daysUntilStale: 180
+   # Number of days of inactivity before a stale issue is closed
+   daysUntilClose: false
+   # Issues with these labels will never be considered stale
+   exemptLabels:
+     - 1.severity: security
+   # Label to use when marking an issue as stale
+   staleLabel: 2.status: stale
+   # Comment to post when marking an issue as stale. Set to `false` to disable
+   markComment: >
+     Thank you for your contributions.
+
+     This has been automatically marked as stale because it has had no
+     activity for 180 days.
+
+     If this is still important to you, we ask that you leave a
+     comment below. Your comment can be as simple as "still important
+     to me". This lets people see that at least one person still cares
+     about this. Someone will have to do this at most twice a year if
+     there is no other activity.
+
+     Here are suggestions that might help resolve this more quickly:
+
+     1. Search for maintainers and people that previously touched the
+        related code and @ mention them in a comment.
+     2. Ask on the [NixOS Discourse](https://discourse.nixos.org/).
+     3. Ask on the [#nixos channel](irc://irc.freenode.net/#nixos) on
+        [irc.freenode.net](https://freenode.net).
+
+   # Comment to post when closing a stale issue. Set to `false` to disable
+   closeComment: false
+   ```
+
+# Drawbacks
+[drawbacks]: #drawbacks
+
+People will need to indicate their interest twice a year.
+
+Marking issues stale might dissuade contributors who already feel
+their contribution was being ignored.
+
+# Alternatives
+[alternatives]: #alternatives
+
+1. Do nothing