Add/Improve documentation

[lost1227]

We need more documentation in several areas:

1. The README should show off attendance-app: what it is and what it does.
2. The development environment instructions are very barebones and could be more fleshed out.
3. It would be nice to have some documentation of project architecture, such as the difference between the api/web, and the structure of code in both the api and in the web.
4. It would also be nice to have some documentation of how to configure the deploy script.
5. It would be nice to have some documentation of how to update dependencies, especially when dependabot alerts us to new security vulnerabilities.