when pointing folks to install the Dart Debug Chrome extension, include a link!

[kevmoo]

So folks can find it fast!

Use https://goo.gle/dart-debug-extension – so we can change it after the fact and track usage

CC @jacob314

[annagrin]

@kevmoo do you know where we are pointing automatically?

[kevmoo]

We just say "install the extension" – we don't give any guidance!