Nexus: Print warning for the Nexus user before pwscf rsync

[aannabe]

Proposed changes

When a new NSCF is located on a different path than SCF, Nexus will rsync the SCF results into the new path. This is a great feature for submitting multiple NSCF calculations with various k-points. However, this can take quite a while and can give the false sense that Nexus is hanging when, in fact, it is silently rsync'ing the results. This has confused me a few times.

I simply put two print statements warning the user that this is happening. It only executes the first time when the directory does not exist. There is probably a better way to output this - let me know if there is and I will be happy to update.

Does this introduce a breaking change?

• No

What systems has this change been tested on?

All Nexus tests pass on my laptop (Linux Mint 21.3), except for 61/69 qdens_radial.

Checklist

• Yes. This PR is up to date with current the current state of 'develop'