Update scrapy command line doc with additional scrapy parse options

Added several options to scrapy command line (parse command) that weren't reflected in the docs.

Some observations:

* I've modified the description of the --spider argument from the one availabe in the scrapy built-in help "use this spider without looking for one". I think my description is more accurate, but I can change it back if you think it's not. If my description is really better I can have it applied to the built-in help of the scrapy coomand.

* I've included placeholder arguments for the added options that support/require arguments. I can reflect it on the other options or I can remove them altogether from the ones I've added. I think adding them better reflects actual usage.