Add namespace to documentation + Enforce `MultiJson` usage

[BuonOmo]

Hi,

I've made a PR for two distinct reasons (hence the two commits!)

Add namespace to the readme 08c8eaf It seems like a pretty valid config, let's expose it!

enforce MultiJson usage 6cfb105 This allows users to always have their chosen implementation used. And gives a more consistent behavior.

Thanks for the great tool 🚀

[michaelklishin]

Thank you!