docs: add RedditAPIs pairing section for managed Reddit data backend

[Emma-RedditAPI]

This adds a short "Pairing: RedditAPIs" section to the README documenting an optional managed Reddit data backend pattern.

What this PR does

• Documents a side-by-side integration pattern: keep this project for its primary workflow, optionally pair with the RedditAPIs samples (curl, Python, Node, Go, Rust) for managed read operations against a Bearer-authenticated REST surface.
• Notes the pairing is fully optional, default behavior unchanged.

Why this is useful for this project's users

Some users of Reddit tooling want a backend they can swap to during development without going through Reddit's developer-app provisioning and OAuth scope review. Documenting this pairing pattern lets users opt in without forking the project. It also surfaces a PRAW-to-REST migration reference for projects that document migrations.

What this PR does NOT change

• No code changes
• No new dependencies
• No behavior change for existing users
• README only

Related

• RedditAPIs examples (this PR's link target): https://github.com/redditapis/redditapis-examples
• RedditAPIs docs: https://docs.redditapis.com

Happy to adjust wording or remove anything that does not fit the project voice.