Add note regarding file system support to README

After an unclean termination of a service, QueueFile failed to peek and remove, yet the enqueue functionality continued to work.  I tweaked the header value for first element position to bypass the corrupt entry.  In looking at the code, I see comments making it quite clear this can happen, yet the README does not.

Is journaling, as noted in the comments, something on the roadmap?
`so this class` should probably be clarified since its outside of QueueFile.