Sync the hbck2 README page and hbck2 command help output

There are major differences in the hbck2 README.md and the command help output, hence we should sync them across for all commands.

Ideally, it should be same as the output of hbck2 help command for ease of maintenance. 

Also few new commands like recoverUnknown and regionInfoMismatch are missing, making users unaware of existence of those.