Add documentation for the new Disk flags and usage

Please add documentation to FAQ on WIKI regarding how to use the new disk-related flags, give examples for:
1. Create and use local SSDs on GCP, AWS, and Azure to run one of the NoSQL benchmarks.
2. Create and use "remote" disks on GCP, AWS, and Azure to run the FIO test.

And then link the FAQ/wiki page from the "./pkb.py --help" text. (To add content to the --help text, look at existing code where "sys.modules['**main**'].**doc** " is changed)