additional/custom R packages for spack, e.g.,

• TMB
• INLA
• eppasm
• naomi

clone this repo to, for example, spackr, then edit the default repos located at etc/spack/defaults/repos.yaml, changing from

repos:
- $spack/var/spack/repos/builtin

to

repos:
- ~/spackr
- $spack/var/spack/repos/builtin