add docs for how to create draft plugins

[michelleN]

@bacongobbler just added support for running powershell scripts on plugin hooks. We should write some docs up explaining how to create a draft plugin from scratch and with the additional info on windows support.

[michelleN]

just kidding found the dep for it

[radu-matei]

Should we keep this issue or #540? 😄

[bacongobbler]

We should keep this one open since it has more background context. I just closed #540. Thanks for pointing that out!