Add issue template and other fixes

Author: mosuem

.github/ISSUE_TEMPLATE/pubspec_parse.md

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

pkgs/pubspec_parse/pubspec.yaml

@@ -3,7 +3,7 @@ version: 1.4.0-wip
 description: >-
   Simple package for parsing pubspec.yaml files with a type-safe API and rich
   error reporting.
-repository: https://github.com/dart-lang/pubspec_parse
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/pubspec_parse
 topics:
 - dart-pub