supervisor should write to $PWD by default

[noblem]

Presently the default behavior with supervise is that it writes the checkpoint JSON file to

$HOME/.fiss/monitor_data.json

which makes it very easy for supervise runs to step on each others toes, become corrupted or entirely overwritten. The default should be wiser and write to $PWD or some other spot that is not guaranteed to blow away the results of other supervise sessions.