[DOCS-3658] docs: Update CDC terminology in README

[jrodewig]

Description

Updates the README's streaming section to use:

• New CDC terminology (stream token -> event source)
• New eventSource() and eventsOn() FQL methods

Motivation and context

This aligns the README with the latest terminology in the docs and FQL.

How was the change tested?

N/A

Screenshots (if appropriate):

Change types

• • [ ] Bug fix (non-breaking change that fixes an issue)
• • [ ] New feature (non-breaking change that adds functionality)
• • [ ] Breaking change (backwards-incompatible fix or feature)

Checklist:

• • [ ] My code follows the code style of this project.
• • [x] My change requires a change to Fauna documentation.
• • [x] My change requires a change to the README, and I have updated it accordingly.

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