Update documentation with the config file details

[edevenport]

The documentation should be updated to include information about the config file support added in PR #63.

I would recommend an example under the Authentication section describing the default config file path, name, and format.

@bdrung - Thank you for the new enhancements. If you do not have time to update the README itself, would you be able to add some notes to this issue about the config file support? This should make it easier for someone else to update the documentation accordingly. Thanks again.

[bdrung]

Quick comment: default config file path is determined by appdirs (to work on all platforms). The format is an ini file. It stores the username (but you could also store the password - the keyring is preferred). The user is asked for the values if they are not present.

I'll try to find some time for the documentation update. I am happy to review and refine documentation updates.