docs: fix order of events in zola overview (templates, server, content)

[iamorphen]

Introduction

Fixes #2441 . This change targets master since it's a documentation fix.

Documentation changes

1. Base overview (and linked installation instructions) on zola 0.19.1 (bumped from 0.17.1). Please note that I did not check all installation routines for correctness.
2. Move creation of all templates first, then start the development server, then create site content.
3. Reword sections in the template portion to allude to details to come in the content portion. The documentation previously grouped individual templates with content using such templates.
4. Remove bash from code blocks that are not shell script source code.
5. Make some long lines in code blocks shorter to remove the need for readers to scroll horizontally.

[iamorphen]

@Keats , I got a little carried away and made some other stylistic changes (line length, bash stuff, noted in the description). If it's better I leave those out, I'm happy to do so. Thanks always!

[Keats]

Thanks!

[iamorphen]

Thanks for your time!