Add hello world to quickstart

[mintlify-development]

Added 'hello world' text to the quickstart.mdx file as requested.

---

Note

Low Risk
Documentation-only text change with no functional or runtime impact.

Overview
Adds a single "Hello world!" line near the top of quickstart.mdx immediately after the introductory paragraph.

^{Written by Cursor Bugbot for commit 348defb. This will update automatically on new commits. Configure here.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is OFF. To automatically fix reported issues with Cloud Agents, enable Autofix in the Cursor dashboard.}

[cursor]

Test placeholder text accidentally committed to documentation

Medium Severity

The text Hello world! appears to be test content that was accidentally committed to the production quickstart documentation. It sits without context between the introduction and "Before you begin" section, disrupting the professional flow. Notably, "Hello world!" is used later in this same document as an example of what users write when following the tutorial, suggesting someone tested the editing workflow and forgot to remove their test change.