Feature Request: Warning when no deployment method is selected

As reported [on TRF](https://www.rocketryforum.com/threads/announcement-openrocket-version-22-02-public-beta-3-is-now-available.171295/post-2280174), some people overlook adding a deployment method, which causes the 'Velocity at Deployment' to show "N/A". Adding a warning about this could solve some confusion.