Fix a regression in doc/www/software.html.  It looks like the link to 'spack-issues.html' was removed in a recent merge.
Fix a regression in doc/www/software.html.  It looks like the link to
'spack-issues.html' was removed in a recent merge.

HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit