Add links to Greg Wooladge's and Bash Hakers wikis

Greg has assembled one of the greatest guides and FAQs about Bash
and shell scripting in general.  It's the must read material for
anybody who does any significant amount of shell scripting.

Bash Hackers Wiki contains loads of verified, up-to-date
information related to Bash and shell scripting.
Merge pull request #7 from mrdeathless/master

Add links to Greg Wooladge's and Bash Hakers wikis