Add Haddock documentation for `RobotRow` fields

[byorgey]

Relevant code pointer:

• Actns: Number of tangible commands invoked
• Cmds: Sum of all commands invoked
• Cycles: Number of times stepRobot has been called
• Activity: Percentage of ticks that this robot was active

We should probably add these as Haddocks here.

Originally posted by @kostmo in #1495