Updated README to refer to signalr branch

[kevinguo-ed]

Purpose

Updated the "Guidance" section to include a link to signalr branch. It provides readers guidance on how to scale token streaming in production.

Does this introduce a breaking change?

[ ] Yes
[X] No

Pull Request Type

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[X] Documentation content changes
[ ] Other... Please describe:

What to Check

• Verify if the description is coherent with the rest of the "Guidance" section.
• Verify if the links to Azure SignalR service and to signalr branch work.