Added rudimentary doc

docs/intervention.md

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+# Interventions
+
+## Overview
+Introducing interventions that affect the relative transmission potential in a given infection attempt, either through relative risk of the susceptible individual or through realtive infecitousness of the transmitter individual.
+
+## Intervention manager
+This trait extension on `Context` allows for querying population by infecitous status and facemask status.
+We introduce the symmetrical function `query_relative_infectiousness` that uses a nested `HashMap` to ascertain the relative change in transmission potential. Taking a person Id, we obtain the facemask status and infectious status to query the float that determines risk. The `register_intervention` function then allows the nested `HashMap` to be created, registering the facemask and infectious status with the intervention container.
+
+## Facemask Manager
+Facemasks  are currently randomly assigned at a given maskiong rate specified in the parameters input JSON using the `assign_facemask_status` function. The `init` function registers facemask and infectious status types to their respective relative transmission potentials and then assigns individuals to either have `Wearing` or `None` for the facemask intervention.
+
+## Impact on transmission
+Currently, the relative transmission potential effet of interventions are deployed in the `evaluate_transmission` function of the transmission manager. Now, the probability of a successful transmission event depends on the additive relative transmission potential of the transmitter and contact as a result of the intervention.