Add feedback telling the player why a rocket launched.

[sparr]

Especially the first launch. I was surprised and confused when my first rocket launched as soon as I put cargo in it. In hindsight, it launched because I had previously "created" a space platform in the map interface, which was waiting for a rocket to deliver the starter pack, but that was not at all clear to me at the time, and the two things were far enough apart that I didn't immediately remember having done it.