[Doc] Remove bad indication for "yarn create react-admin@latest"

[erwanMarmelab]

Problem

yarn create react-admin@latest doesn't work but we document it

Solution

document yarn create react-admin@latest instead

Additional Checks

• The PR targets master for a bugfix or a documentation fix, or next for a feature
• The documentation is up to date

[fzaninotto]

You need to update the CreateReactAdmin.md and the Readme.md, too.