docs(@nylas/connect): rewrite README

Restructures the README onto the house style shared by nylas-nodejs,
nylas-python, nylas-ruby and nylas-java, and fixes several claims that
did not match the source:

- The first usage example read `result.email`, which does not exist on
  `ConnectResult`. The address is on `result.grantInfo`.
- The config table listed 6 of the 11 `ConnectConfig` options, omitting
  `identityProviderToken` among others. All 11 are now documented.
- The identity-provider section was appended below the FAQ under a
  second `# H1`, with a second `## Error Handling`. Both are folded in.
- The error section now distinguishes the 6 exported error classes from
  the 9 `OAuthError` subclasses, which are thrown but not exported and
  so must be narrowed with `error.name`.
- The stated runtime was "Node.js 18+", which src/crypto/pkce.ts cannot
  honour: it calls `crypto.subtle` and `crypto.getRandomValues` on the
  bare global, with no polyfill and no `node:crypto` import. Now 22+,
  matching the root README.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: nbarraclough

.changeset/nylas-connect-readme-rewrite.md

@@ -0,0 +1,5 @@
+---
+"@nylas/connect": patch
+---
+
+Rewrite the README. The previous version's first example read the mailbox address from `result.email`, which does not exist on `ConnectResult`, and its config table documented 6 of the 11 available options.