Extend and improve Qbs documentation

The current documentation is too limited and obscure to actually allow any use of Qbs.

After spending 2 days on it I can't even understand how to print something for debug in a consistent way. For example, is it possible to use console.info when I reparse  a Qbs project? Where do I put it to not get parsing errors?

Anyway, all started because I wanted to generate a header file with some info retrieved from git.

I barely managed to get to the part where Qbs generates a file using a Rule, but there are so many things I don't understand I had to give up. For example:

• How to run Qbs code  when parsing a Qbs project?
• How to access sourceDirectory in a Rule?
• What should I use to run git from Qbs? A Command or a Process service?
• How do I use a Process Service? Do I need to import something? Where do I put a Process object?
• Can I run a Command and a JavaScriptCommand in a single Rule?
• If not, how do I run git, get its output and use it to write a file?

Maybe things make sense to the people who created Qbs and maybe to the ones that have been using it since its early versions, but for a new user the whole project is pretty much unusable.