doc: README: Update several feature names to sentence case

[jrodewig]

Description

We recently aligned with marketing to use sentence case for several feature names, including "event feed" and "event stream." This updates the README docs.

Motivation and context

Better alignment with marketing and other docs

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.
• • My change requires a change to Fauna documentation.
• • My change requires a change to the README, and I have updated it accordingly.

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