document how to enable schema validation on CI

vscode-yaml is my favourite vscode plugin and I find it extreamly useful for validating various yaml files and ansible ones in particular.

Still, there is one aspect which is not covered by the tool: how to verify schema on an entire repository from the command line, so we can perform the checks on CI servers.

Before someone argues that this may be outside the scope of the extension please note that both kind of validations should be able to use the same configuration. If I set "roles/**/*.yml" to use Ansible schema, I need to be sure that the same setting is used by vscode and the command line call.

Once we have this sorted we should include a section in the main README that indicates on how to use it with automation.

At this moment I am not aware of any way of doing schema validation on CI so thus is why I opened this ticket.

Start by reviewing the main README and the existing schema configuration documentation. Determine whether the current project exposes a command-line path that uses the same settings as vscode-yaml, then document the verified CI usage and shared configuration; if no such path exists, record that limitation rather than describing an unverified workflow.