Add issue template and other fixes

Author: mosuem

.github/ISSUE_TEMPLATE/stream_channel.md

@@ -0,0 +1,5 @@
+---
+name: "package:stream_channel"
+about: "Create a bug or file a feature request against package:stream_channel."
+labels: "package:stream_channel"
+---

pkgs/stream_channel/CONTRIBUTING.md

@@ -3,7 +3,7 @@ version: 2.1.3-wip
 description: >-
   An abstraction for two-way communication channels based on the Dart Stream
   class.
-repository: https://github.com/dart-lang/stream_channel
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/stream_channel
 
 environment:
   sdk: ^3.3.0