Readme points to old docs

[vlkuznet]

Describe the bug

For example the readme states:

Note: Orchestrator functions must follow certain code constraints.

That has a link to: https://docs.microsoft.com/en-us/azure/azure-functions/durable/durable-functions-orchestrations?tabs=csharp#orchestrator-code-constraints

That has since been broken out into a separate page of docs, here: https://docs.microsoft.com/en-us/azure/azure-functions/durable/durable-functions-code-constraints

That should be a pretty straightforward change.

[davidmrdavid]

Thanks @vlkuznet, I'll be tracking this documentation update :)