Added pictures to game rules overview.

Map view icons are currently hotlinks to the repository. Closes Starstrider42/RemoteTech#10.
Added pictures to Flight Computer guide.

Note: The attitude control section does not match how the game behaves, particularly with respect to the TGT attitude mode. I'm assuming that the behavior described in the guide is intended, and that the unusual behavior of TGT mode is a bug; see RemoteTechnologiesGroup/RemoteTech#69.
Fixed errors in re-entry tutorial.