Markdown fixes for developer setup

This branch contains several Markdown-related fixes for the developer setup instructions, including:

1. Proper order of headings
2. Alignment of pre blocks within bulleted lists
3. Unordered list under Fedora changed into an ordered list (as it contains steps
4. Removal of `postgresql` and `postgresql-libs` as they're pulled in as dependencies anyway — this allows all the lines in that pre block to be shorter (as comments are aligned), so that lines do not wrap
Not sure what you mean by "OSX uses zsh".  OSX uses bash by default, but from a markdown perspective, we're just saying "in a shell"