Add featured commands in readme

[ernilambar]

Fixes https://github.com/wp-cli/scaffold-package-command/issues/227

• This will read commands from extra.featured-commands from composer.json and add anchored links in the Using section in the README file.

Note: I could not find a way to add feature test for this as commands are not returned in Behat test currently.

[danielbachhuber]

wontfix https://github.com/wp-cli/scaffold-package-command/issues/227#issuecomment-1972989717