[1-Pager] Side Input Architecture

[Kenneth Knowles <kl...@google.com.INVALID>]

Hi all,

Luke & I put together a 1-pager* with lots of diagrams that just goes into
some more detail on the runner-independent side input story for the Beam
Runner/Fn API.

    https://s.apache.org/beam-side-inputs-1-pager

Here is the teaser line:

"What happens when a user requests to side input a PCollection? What does
the user provide? What does the SDK provide? What does the runner provide?
What is a PCollectionView?"

I hope this helps all runner authors (and other interested folks) and maybe
starts some discussions. Please take a look!

Kenn

*actually 2.5 pages