update readme with misc improvements

[mykmelez]

Here are a variety of improvements to the README that I made in the process of configuring the project to use its command-line interface on my client.

The only change I'm uncertain about is the change to the mysql line that creates the database. Update: it looks like the line assumes an apk user, so I added lines to create that user and grant it privileges on the database.

[ozten]

Thanks for testing and improving these instructions.