Update documentation with LACONIA_NO_CALLBACK

[hugosenari]

Since #48 resolution, a new env LACONIA_NO_CALLBACK, we need document this behavior.

Without env: LACONIA_NO_CALLBACK='true'

cont app = (event, laconiaContext, callback) => {};
exports.handler = laconia(app); 

With env: LACONIA_NO_CALLBACK='true'

cont app = (event, laconiaContext) => {};
exports.handler = laconia(app); 

laconia-core ignore callback parameter passed to handler.