Recommend BOUT-configs?

[johnomotani]

Maintaining configurations for various HPC clusters in BOUT-configs has proved to be useful. Should we recommend and link to it from the "machine specific installation" section of the manual?

If we want to do this, it would be good to resolve boutproject/BOUT-configs#2...

[ZedThree]

We could probably even delete that whole section and just link to BOUT-configs