Symlink README.pod -> lib/Test/Given.pm

This gives your project a more polished appearance in Github,
and saves you from having to manage two sets of identical
documentation.

Note that this commit kills the default README, which contains
installation intructions. I didn't bother adding them to l/T/Given
because I think most Perl devs know how to install CPAN libraries
now - particularly those interested in using different testing
libraries. At least that's my own justification for not bothering
putting it into my own CPAN modules :)