replace npx directus by npx d9

[louisdussarps]

Change description

Replace npx directus by npx d9 in the documentation

Type of change

Renaming

Checklists

Development

• Lint rules pass locally
• Application changes have been tested thoroughly
• Automated tests covering modified code pass

Security

• Security impact of change has been considered
• Code follows company security practices and guidelines

Network

• Changes to network configurations have been reviewed
• Any newly exposed public endpoints or data have gone through security review

Code review

• Pull request has a descriptive title and context useful to a reviewer. Screenshots or screencasts are attached as
  necessary
• reviewers assigned
• Pull request linked to task tracker where applicable