Docs need to mention null usage for initialVariables

[RavenHursT]

The docs for setting initialVariables for the Container API do not mention how to initialize unknown values for variables (i.e. The initial cursor value for pagination).

The correct way to initialize variables w/ an unknown value is to use null. It took over half a day of searching and asking before this answer was given to me:

http://stackoverflow.com/questions/34406667/relay-pagination-how-to-initialize-after-value/34407181#34407181

This should definitely be in the documentation for this feature.

[devknoll]

@RavenHursT This is technically true, but I'm curious: why are you managing the after cursor yourself? Relay will automatically add the argument and its value when you change the first variable.

[RavenHursT]

@devknoll : Server-side rendering.. if I go to www.mysite.com/widgets?pageNumber=5 then we need a way to initialize what will be rendered when using https://github.com/denvned/isomorphic-relay