Top level subsystem folders in the quickstart repo are missing README.md files (except XTS).

Use the XTS README.md as an example of what they should look like. I suggest the workload assignments for completing this task as follows:

ArjunaCore - Mike
ArjunaJTA - Mike
ArjunaJTS - Mike
atsintegration - Mike
ObjectStore - Mike
blacktie Amos
rest-tx - Mike