Add insight preview tool, nk-md, to curriculum-tools

[lizTheDeveloper]

Add the insight preview tool to curriculum-tools, such that when you npm install -g curriculum-tools you can use the command nk-md right away.

https://www.npmjs.com/package/nk-md

Don't deprecate the original package, we want people to be able to install it separately.

[nem035]

enkitest codebase has a lot of work done for this, we might wanna chat about it :)