Document the configuration file and options for customizing doT parser

[rameshdavid]

Looking at the code here it seems like InGenR uses cosmiconfig to support a configuration file, however this is not documented at all.

I think this is particularly important because by using the config file we can change the dot template delimiters for languages where the default delimiters are problematic (the templates need a lot of escaping).

[lorefnon]

Yes, this project is very new and not many features are well documented.

If you'd like to contribute a PR for this I'd really appreciate it.