Add Tools section for Bash
Add command-line usability blog post link
Add link to shunit2 in bash README.md
Merge pull request #8 from mbbx6spp/add-bash-linters

Add Tools section for Bash
Add 'Things You Should Know In Bash' section

Includes:
* Initial cut of section
* Updates based on feedback from @polynomial.
* Add subsection on locals and arrays