docs(identifiabl): fix Quick Start to use the real export name

[davidcrowe]

Problem

The identifiabl README's Basic Usage (and three later examples) import and call createIdentifiablMiddleware — an export that does not exist. The package exports identifiabl(config) (the Express middleware) and createIdentifiablVerifier(config) (the non-Express verifier). A reader copy-pasting the Quick Start fails at the very first line:

import { createIdentifiablMiddleware } from '@gatewaystack/identifiabl';
//       ^ not exported

For the identity layer that the whole stack builds on — and during a repo-visibility push — a broken headline example is exactly the wrong first impression.

Fix

Rename all five occurrences to identifiabl. The documented config (issuer/audience/jwksUri) already matches IdentifiablConfig, and identifiabl() sets req.user exactly as the surrounding prose describes, so no other changes are needed. Verified the built dist exports identifiabl.

Docs-only; no code or version change.

[davidcrowe]

Reviewed + confirmed green (MERGEABLE/CLEAN). README Quick Start now uses the real export identifiabl(...) instead of the nonexistent createIdentifiablMiddleware(...) — matches the actual export.

@davidcrowe — needs your merge. No version bump here, so no republish is strictly required; the corrected README will reach npmjs.com on identifiabl's next publish.