Add issue template and other fixes

Author: mosuem

.github/ISSUE_TEMPLATE/os_detect.md

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

pkgs/os_detect/pubspec.yaml

@@ -1,7 +1,7 @@
 name: os_detect
 version: 2.0.2-wip
 description: Platform independent OS detection.
-repository: https://github.com/dart-lang/os_detect
+repository: https://github.com/dart-lang/core/tree/main/pkgs/os_detect
 
 environment:
   sdk: ^3.0.0