🐛 BUG: Fix minor typo in chanfana-openapi-template README: incorrect template path in C3 command

### Which template does this pertain to?

chanfana-openapi-template

### What versions are you using?

latest

### What operating system and version are you using?

N/R

### Please provide a link to a minimal reproduction (optional)

_No response_

### Describe the Bug

The **Getting Started** section in the README.md of the `chanfana-openapi-template` contains an outdated/incorrect example command for creating a new project using C3.

**Current text (incorrect):**
```
Outside of this repo, you can start a new project with this template using C3 (the create-cloudflare CLI):
npm create cloudflare@latest -- --template=cloudflare/templates/openapi-template
A live public deployment of this template is available at https://openapi-template.templates.workers.dev/
...
```

This points to `cloudflare/templates/openapi-template`, which is not the correct path for **this** template.

**Expected / Correct command:**
```bash
npm create cloudflare@latest -- --template=cloudflare/templates/chanfana-openapi-template
```

**Why this matters**
Users following the README will scaffold the wrong template (likely an older or different OpenAPI variant), leading to confusion and wasted time. Updating this one line would make the template immediately usable via C3 as intended.

**Suggested fix**
Replace: `--template=cloudflare/templates/openapi-template` with `--template=cloudflare/templates/chanfana-openapi-template`

**Additional context**
Repository: https://github.com/cloudflare/templates/tree/main/chanfana-openapi-template
File: README.md
No other changes needed — the rest of the README looks accurate and helpful.

Thanks for maintaining these excellent templates — this is a very small tweak that would improve the onboarding experience significantly!

### Please provide any relevant error logs

_No response_