1. Addition of *Running Jekyll on Ubuntu* section, to address Ubuntu stumbling block as per https://github.com/jekyll/jekyll/issues/5719.
2. Restructuring, and I hope I understood correctly when NodeJS/Python are/aren't required.
3. Gentler wording – it's probably not a good idea to tell punters who hit this page because they ran into trouble that installing Jekyll *is* easy and straight-forward; it *ought to be* straight-forward. (There's always the potential for pain and confusion if not all dependencies are in place.)