Add discussion of cost-benefit calculus of activists

[iangow]

@sapyung says

Shall we talk about why the activists would seek board seats (incentive/cost-benefit) and why the managers would grant board seats (incentive/cost-benefit)? We only talk about the cost of being an activist director, not why they actually want to get board seats. Maybe they can come after introduction.

[iangow]

See reading material under #88.

[iangow]

Paper submitted.