Document use of dosarray_synch_time.sh

[niksu]

Info on motivation+usage of https://github.com/niksu/dosarray/blob/bb4f0a980829a1c360563ca6e3990bcc66b596c5/src/dosarray_synch_time.sh could be added to https://github.com/niksu/dosarray/blob/bb4f0a980829a1c360563ca6e3990bcc66b596c5/doc/USAGE.md

[shilpiBose29]

I think it would be best to document this after the load measurement changes because they are related