at_cli not working as expected

[cconstab]

Now under #86
The at_cli tool feels unfinished and very buggy. There are no instructions on how to use.
This is both bugs and feature requests (features arguably should already be here)

To Reproduce
Steps to reproduce the behavior:

1. Clone the repo
2. pub get
3. run the main.dart

Expected behavior
I would expect an display of options. I would also expect full documentation and examples in the readme.md

Screenshots

cconstab@cally:~/at_tools/at_cli$ dart bin/main.dart
Unhandled exception:
FileSystemException: Cannot open file, path = 'bin/@alice' (OS Error: No such file or directory, errno = 2)
#0      _File.throwIfError (dart:io/file_impl.dart:635:7)
#1      _File.openSync (dart:io/file_impl.dart:479:5)
#2      _File.readAsBytesSync (dart:io/file_impl.dart:539:18)
#3      _File.readAsStringSync (dart:io/file_impl.dart:584:18)
#4      AtCli.getAuthKey (package:at_cli/src/at_cli.dart:109:29)
#5      AtCli.init (package:at_cli/src/at_cli.dart:18:19)
#6      main (file:///home/cconstab/at_tools/at_cli/bin/main.dart:19:15)
#7      _delayEntrypointInvocation.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:281:32)
#8      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:184:12)
cconstab@cally:~/at_tools/at_cli$

Additional context
Add any other context about the problem here.