Include some benchmarks or use cases in the README

[colindean]

I'd love to sees some benchmarks comparing other common ways of doing this that can be accomplished with commonly-installed tools, e.g. my own yaml2json in Ruby.

(I'm semi-volunteering to do this but admittedly it's low priority)

[colindean]

I knew I'd done something in Python at one point and randomly found it while looking for something else just now: https://github.com/pittmesh/pittmesh.net/compare/json2yaml#diff-e5a185fb5404918fbc8d4910b2950904

[bruceadams]

I will admit that performance is not a huge interest of mine for yj. I just presume it's quick, given the libraries I'm using. I'm much more interested in what yj might do with the many complex things one express in yaml. This, of course, is mostly a question of: What does serde_yaml do with complex yaml input?