Use `getpapers` `<...>` style for values

[petermr]

Please use the <...> notation for option values in the --help. See, for example getpapers -h or pip -h for examples

  --proxy <proxy>             Specify a proxy in the form [user:passwd@]proxy.server:port.
  --retries <retries>         Maximum number of retries each connection should attempt (default 5
                              times).
```.


The use of capitals often implies a LITERAL constant

[ayush4921]

Need help with doing this. Can anyone suggest how this can be implemented in argparse.