[rancid] Rancid 3 documentation tweak

[Howard Jones]

The README for RANCID 3.0 says that perl5 or greater is required to run 
RANCID. In fact, it's perl 5.10 or greater, which is significant for 
some. For example, current CentOS 6 (and I guess RHEL and Scientific 
Linux too) come with perl 5.8.8, so it requires a separate perl install 
just for RANCID. (installing it over the system perl leads to fighting 
between CPAN and yum)

Related: a configure option to specify the location of the perl 
interpreter would be handy!

Cheers,

Howie