Document how component and template interact

[joelhawksley]

Problem statement

As a consumer of ViewComponent, it can be difficult to understand the functional relationship between the component and template:

• Are instance variables from the component accessible in the template?
• What about instance methods?
• Do instance methods need to be public to be accessible in the template?
• What helpers are accessible?

Proposed solution

Add an explanation, potentially as an entirely new page? (Encapsulation?)