Create new exercise on effect of positive feedback on load disturbances [principles]

[Richard Murray]

In Ch 2 (principles), Section 2.1 (nonlinear static models), we show that with negative feedback you can decrease the effect of disturbances. There is a comment at the end that talks about an exercise determining the effect of positive feedback on load disturbances. This is currently missing.

Karl has this on his plate to take care of. Worst case, we remove the sentence.

[Richard Murray]

Addressed in fbssolns commit 1a08b7f, which is part of commit f16bf49.