Delete vnext\README.md and create a build task to copy the root one to vnext\ #4632
Description
Yeah, according to @acoates-ms the vnext readme drives what shows up in the package:
The one in vnext will show up on npmjs.org for the published npm package, since its part of the actual npm package.
The one in the root is the one that will show when people go to the GitHub repo. The one in vnext is the one they will see on npmjs.org. If we want them to be the same, we should probably just delete the one in vnext, but ensure that we have a build step to copy the one in the root into vnext before publishing.
Since the vnext readme is out of date, let's delete it and replicate the main readme over.