- [x] add `concretize.lp`, `spack.yaml`, etc. to licensed files
- [x] update all licensed files to say 2013-2021 using
`spack license update-copyright-year`
- [x] appease mypy with some additions to package.py that needed
for oneapi.py
#11152 added documentation for #8772 but some details were based on
an earlier implementation that had changed by the time #8772 was
merged. In particular, #11152 mentioned that upstream Spack instances
were configured in config.yaml, when in fact they should be placed in
a separate upstreams.yaml config file; this PR updates the
documentation accordingly.
