Issue Description:

I had to discover https://github.com/apple/swift-package-manager/blob/main/Documentation/Usage.md, which looks incredibly useful, by googling. Apparently❓ this is the only place where the swift package edit command (for example) is actually described. When you do {{swift package edit -help}}, it doesn't really tell you anything. Please include the contents of that usage document from what you get with the -help option.

Please also link this document or include it in the official docs at https://swift.org/package-manager/. This is probably the 10th time I've tried to find the information in that document; not being able to find out how things work through the official channels is really frustrating!