Ways to contribute

### If anyone is interested in helping out, here are a number of ways you can jump in:
#### Write more exercises.
- Ideally, we would have 3-5 exercises for each aspect of each major topic presented. This gives students the chance to do an exercise or two with help, and then complete another exercise or two independently. The goal is that students can solve at least one exercise in each section independently.
#### Write more challenges
- Exercises ask students to write a small program that demonstrates competence with one particular skill or concept. Challenges ask students to combine different skills, or use new skills to implement developmentally appropriate versions of their own ideas.
- Challenges can be written in any section, right after the Exercises for that section. It would also be good to develop a good set of interesting Challenges at the end of each notebook.
#### Write up a project
- Now that the Python essentials are mostly written, the interesting work is writing up projects that people will want to complete. Propose a project, and write a notebook that shows people how to complete the project.
#### Proofread for accuracy
- If you have a solid understanding of programming skills and concepts, I'd love to hear feedback about anything that could be explained more clearly, or more accurately.

@ehmatthes