Docs - Basic cleanup

Created by: kghopson

Make the following basic changes to the documentation. Ideally, front page first, then work through all existing documentation.

- Indent paragraphs after headings, based on position in outline (nevermind, will probably require new server)

• General cleanup to all pages linked from about.sourcegraph.com: - Code search docs - Code intelligence docs - Campaigns docs

Quickstart page

• Quickstart page should appear on side nav menu - Reorganize quickstart page @ Core Documentation heading to match documentation outline in side nav - Reorganize quickstart page (general) for better flow