Fix typos in tutorial

parrent > parent, url > URL
Requirements made slightly more complete: cf https://github.com/ianmiell/shutit/blob/master/library/jq/jq.py
Add --argjson, fix #648
Fix #647, but caused by 89791a0
Add until(cond; next); fix #639
Merge pull request #616 from ianmiell/ianmiell_requirements

Requirements made slightly more complete
Merge pull request #611 from StevenMaude/tutorial-typo-fixes

Fix typos in tutorial
Fix #649