WIP: Streamlining current sections and adding new ones

Edit: I've inserted what I've been working on offline. I want to make sure I'm going in the right direction, so feedback would be appreciated.

I've rewritten the first paragraph to clarify why workflows are important.

I'm new here, so I'm not sure where to ask questions or discuss documentation. I want to talk about the focus/goal of the "Common Workflows" section and argue that it seems incomplete.

That being said, I think the "Colorizing line art" and "Creating pixel art" can stand on their own as tutorials, while the current "Speed Painting" and "Painting" sections can be grouped under an umbrella "Painting Workflows" section.