Update new issue template.

- Clarify which products are developed in the SDK repo and point to
  other repos for relevant stuff.
- In particular, route language issues to language repo.

Change-Id: I36c9c2108a67d8131d2c6e7641d34bf31745843d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/100887
Auto-Submit: Bob Nystrom <rnystrom@google.com>
Reviewed-by: Aadil Maan <aadilmaan@google.com>
Commit-Queue: Bob Nystrom <rnystrom@google.com>

.github/ISSUE_TEMPLATE.md

@@ -1,6 +1,26 @@
 Thank you for taking the time to file an issue!
 
-In order to route, prioritize, and act on this, please include:
+This tracker is for issues related to:
+
+* Analyzer
+* Common Front End (CFE) and kernel
+* Dart core libraries ("dart:async", "dart:io", etc.)
+* Dart VM
+* dart2js
+* dartfix
+* dev_compiler
+
+Some other pieces of the Dart ecosystem are maintained elsewhere. Please
+file issues in their repository:
+
+* Dart language: https://github.com/dart-lang/language
+* Dart website: https://github.com/dart-lang/site-www
+* Flutter: https://github.com/flutter/flutter
+* Linter: https://github.com/dart-lang/linter
+* dartfmt: https://github.com/dart-lang/dart_style
+
+If you aren't sure, file the issue here and we'll find the right home for it.
+In your issue, please include:
 
 * Dart SDK Version (`dart --version`)
 * Whether you are using Windows, MacOSX, or Linux (if applicable)
@@ -9,13 +29,10 @@ In order to route, prioritize, and act on this, please include:
 Missing some or all of the above might make the issue take longer or be
 impossible to act on.
 
-----
+If you simply have a question, consider starting with Stack Overflow:
 
-Is it really an issue? For general questions consider starting with Stack
-Overflow:
 https://stackoverflow.com/questions/tagged/dart
 
-Also consider our Gitter channel for light-weight/quick discussions:
-https://gitter.im/dart-lang/sdk
+For a real-time response, consider our Gitter channel:
 
------
+https://gitter.im/dart-lang/sdk