docs(select): update markup to include new selectedText container
docs(select): update markup to include new selectedText container

BREAKING CHANGE: selected text node now needs to be wrapped in an outer `mdc-select__selected-text-container` span; see README for updated markup

PiperOrigin-RevId: 331237284

material-components/material-components-web,material-components/material-components-web,material-components/material-components-web