docs: README: Update several feature names to sentence case

[jrodewig]

Problem

Two unrelated changes (bundling cause it's just README):

• Per update package.json engine fauna-shell#579, we recently bumped Node versions for CLI v4:
  • Required: v20.18 or later
  • Recommended: v22 or later
• We recently aligned with marketing to use sentence case for several feature names, including "Region Group."

Solution

Updates the README.