Most top level subsystem folders in the quickstart repo are missing README.md files

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