Link to Axios documentation for config options

[robinheinze]

We frequently get questions about how to override various Axios config options in the 3rd parameter.

We mention it in the README here, but I think it's easily glossed over.

I think it could help folks to point them to the Axios docs that list all the various options for that config object (https://github.com/axios/axios#request-config).

Also, to specifically call out that the config object can be used for the most common scenarios we get asked about:

• Passing query string params with a post request
• Passing a data body with a delete request

[robinheinze]

Having this updated in the README would help address things like #177