Clarify scoring in shared autonomy challenge (#155)

Clarified own goals and scoring once messages exceeded.

challenges/shared_autonomy_challenge.tex

@@ -79,7 +79,8 @@ \subsection{Miscellaneous Notes}
 \item Teams are given wide flexibility in interface implementation with the goal of inspiring innovation in how the challenge is addressed. For instance, a team could stream images from the human-operated robot but may face low bandwidth at the venue  (Note, the rules do not specify that any special effort will be made to provide stronger bandwidth for the challenge). Due to bandwidth constraints, teams may prefer to process images on board robot and send high level state info back to operator. However, this forces the operator to work with the robots imprecise state estimation. The choice is left as a research challenge for teams. 
 \item Similarly, no specification is given on what control interface can be presented to the human operator. Teams may choose to directly command walk directions and kicks or to use a mixed autonomy mode where the operator gives high level directives that the human-operated robot implements. The only limitation is that the input from the operator must be some sort of command, i.e., it is not sufficient to only augment the robot's perception or localization.
 \item Finally, the hardware of the interface (e.g., keyboard, joystick, virtual reality headset) is left up to the discretion of teams.
-\item The defending team is not permitted to score because doing so may be too easy to counterattack with long kicks due to the field size and the limited size of teams.
+\item The defending team is not permitted to score because doing so may be too easy to counterattack with long kicks due to the field size and the limited size of teams. As a corollary, the attacking team cannot score own goals.
+\item If the attacking team exceeds its message budget, it may not score points with either goals or passing.
 \item Total expected time per match: 5 minutes (3 minutes playing and 2 minutes set up). 
 \end{itemize}