Updates to the basics page

- Add a git philosophy section
- Add a code example for fetching updates after creating a new branch
- Rewrite the 'Close and Reference Issues with a Commit Message' section
  - Fix some mistakes
    - Cannot close cross-repo issues via commit msg
    - Keyword must be directly in front of the issue reference
  - Add new info
    - Can use short form reference if you forked the repo
    - Cannot close an issue via commit msg if you cannot via github.com
    - Add example links to actual commit messages
  - Simplify some info
    - Ordering of supported keywords is more consistent
    - Put important info in important boxes
Improve wording
Move content from an important box to a footnote

They said the same thing more or less, neater to group them together.