swc-installation-test-2.py: Link directly to install docs

Expecting the Software Carpentry maintainers to keep up-to-date
documentation for each system/package pair is not realistic.  Instead,
link to each package's installation instructions (as best I can find
them).  The system/version/package globbing (using fnmatch, see
glob(7)) makes it easy to setup per-system and per-version URLs if you
want to fine-tune the instructions.