Add more documentation

[panov-andy]

Hi There,

Please, can you add some more documentation about how to setup the development process with your project? I understand that it's something very obvious for node-js developers but not for someone who came from another dev-language. Personally, I want to add my custom export-template and I'm struggling at the moment once I change something how to make test execution and check the results. Even two lines... please :) Or I saw the express server. Can it show the transformation results?

I checked the codebase and I want to say that it really wonders me how elegant your solution is with converting one format to another!! Absolutely simple and amazing!!

Thank you, Andrey.

[bryantgtx]

I would love to see docs on how to use SPOT for:

1. multipart forms (https://swagger.io/docs/specification/describing-request-body/multipart-requests/)
2. dictionaries with variable keys (https://swagger.io/docs/specification/data-models/dictionaries/)

Thanks.

[scal-lider]

I would love some about String format