Add documentation for market share and current hospitalized cases

[jlubken]

Review test with data science, health comm policy.

Market share will result in optimistic capacity projections when it isn't adjusted for failover and influx from neighboring regions/hospital systems or hospitals. e.g. Princeton gets patients from New York.

Current cases will result in pessimistic capacity projections when it does not account for infection clusters. e.g An uptick in infections from members of a retirement community do not reflect the broader impact of social distancing.