Document running Workflow commands against Temporal Cloud

[tlalfano]

Document running Workflow commands against Temporal Cloud

Summary

This adds a short README section that clarifies the relationship between the
Temporal Cloud CLI extension and the regular Temporal CLI Workflow commands.

The README already shows how to install the Cloud extension and authenticate
with temporal cloud login, but users who land on this repository may not know
what to do next when they want to operate Workflow Executions in a Cloud
Namespace. This update adds examples for using temporal workflow list and
temporal workflow start with the same CLI profile and a Cloud Namespace
endpoint.

Changes

• Clarifies that temporal cloud ... manages Temporal Cloud resources.
• Shows that Workflow Execution operations still use temporal workflow ....
• Adds temporal workflow list and temporal workflow start examples using
  --profile, --address, and --namespace.
• Notes that a compatible Worker should be polling the target Task Queue before
  starting a Workflow.

Testing

• README-only change.
• Ran git diff --check.

Drafted with GPT, reviewed by Tasha