Website's quick start doc incorrectly uses `specify --version` instead of `specify version`

[cedricvidal]

Describe the documentation issue

The quick start section on the website instructs users to verify the installation with specify --version. However, the correct command is specify version (without the double dash). This discrepancy may confuse new users who follow the documentation and encounter an error.

Steps to reproduce

1. Follow the documentation to install Spec Kit.
2. Run specify --version as suggested.
3. Observe that the command is invalid and the correct syntax is specify version.

Suggested fix

Update the documentation to instruct users to use specify version instead of specify --version for verifying the installation.

Related context:

• No existing issues about this discrepancy were found.