Clarify a few areas in the README

Make it more explicit for dependencies that one must both ensure they're listed so they get copied, and they must be included on the pages in order to have effect.

Make note of fact that Hologram also parses javascript files for comments.

Make it clear that items in the same category are sorted alphabetically by name
Issue #86: Add documentation related to categories and parent/child relationships

Make it clear that if a child does not have a category, or defines the same category, it will be grouped with its parent. The implication is that if it doesn't have the same category, it will not appear on the same page.

Make note that the category is optional if a component defines a parent.