storage-daemon/qapi/qapi-schema: Add a proper introduction

Contents adapted from qapi/qapi-schema.json.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20250404121413.1743790-11-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
1 file changed