docs: add a link to the spack repo in the PR section
docs: add a link to the spack repo in the PR section

iulian787/spack,mfherbst/spack,EmreAtes/spack,krafczyk/spack,skosukhin/spack,LLNL/spack,TheTimmy/spack,krafczyk/spack,skosukhin/spack,matthiasdiener/spack,TheTimmy/spack,matthiasdiener/spack,skosukhin/spack,mfherbst/spack,lgarren/spack,tmerrick1/spack,krafczyk/spack,LLNL/spack,iulian787/spack,mfherbst/spack,lgarren/spack,LLNL/spack,EmreAtes/spack,matthiasdiener/spack,TheTimmy/spack,skosukhin/spack,LLNL/spack,iulian787/spack,krafczyk/spack,tmerrick1/spack,lgarren/spack,skosukhin/spack,TheTimmy/spack,EmreAtes/spack,tmerrick1/spack,matthiasdiener/spack,mfherbst/spack,EmreAtes/spack,tmerrick1/spack,iulian787/spack,tmerrick1/spack,lgarren/spack,krafczyk/spack,TheTimmy/spack,iulian787/spack,LLNL/spack,matthiasdiener/spack,lgarren/spack,mfherbst/spack,EmreAtes/spack