Update README.md (#2091)

Deprecating the old template and pointing people to the new ones.

*Replace this paragraph with a description of what this PR is changing
or adding, and why. Consider including before/after screenshots.*

*List which issues are fixed by this PR. For larger changes, raising an
issue first helps
reduce redundant work.*

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-devrel
channel on [Discord].

<!-- Links -->
[Flutter Style Guide]:
https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo
[CLA]: https://cla.developers.google.com/
[Discord]: https://github.com/flutter/flutter/wiki/Chat
[Contributors Guide]:
https://github.com/flutter/samples/blob/main/CONTRIBUTING.md

Author: zoeyfan

game_template/README.md

@@ -1,3 +1,7 @@
+The following template will be deprecated soon. Please refer to the new games repo for more genre-specific templates: https://github.com/flutter/games
+For more information, please refer to flutter.dev/games to see all resources available for flutter game developers. 
+
+Old template readme: 
 A starter game in Flutter with all the bells and whistles
 of a mobile (iOS & Android) game including the following features: