Pulp

Add a conceptual introduction to the plugin writer guide. This would help motivate and offer perspectives on some of the most important questions a plugin writer has to answer before coding:

Defining a content type to manage
What is the content called?
What attributes make each piece of content unique?

How will this content get into Pulp?
Upload?
Sync from a remote source?
- what kind of tools can be used to sync from remote?
- download API
- storage API

How does the content need to be published?
Is there metadata that needs to be generated at publish time?
What tools will be used to consume the content?
- does the tool expect static files served by a web server
- does the tool use a protocol other than HTTP to consume content?