CONTRIBUTING.md: fix charter link (s/rfcedtyp/group/)

https://datatracker.ietf.org/rfcedtyp/rswg/about/ is defunct.

Using the generic "group" selector suggested (as more
future-proof than just replacing "rfcedtyp" with the current
"edwg") by Robert Sparks.

CONTRIBUTING.md

@@ -2,7 +2,7 @@
 
 Anyone can contribute to RSWG; you don't have to join the Working Group, because there is no "membership" -- anyone who participates in the work, as outlined below, is part of the RSWG Working Group.
 
-Before doing so, it's a good idea to familiarize yourself with our [charter](https://datatracker.ietf.org/rfcedtyp/rswg/about/). If you're new to this, you may also want to read [an informal guide to the IETF process](https://www.ietf.org/standards/process/informal/) and the [Tao of the IETF](https://www.ietf.org/tao.html).
+Before doing so, it's a good idea to familiarize yourself with our [charter](https://datatracker.ietf.org/group/rswg/about/). If you're new to this, you may also want to read [an informal guide to the IETF process](https://www.ietf.org/standards/process/informal/) and the [Tao of the IETF](https://www.ietf.org/tao.html).
 ## Contributing to Work in Progress
 
 The RSWG is not an IETF Working Group but generally follows IETF procedures as detailed below. The specific process for the RSWG is defined in [RFC 9280](https://www.rfc-editor.org/rfc/rfc9280).