No docs on using native notebooks

[Matelasse]

Hi. I'm using vscode insiders and from the looks of it the native notebook support for ipnbs has been added in the extensions, but there's no documentation on how to enable it.

[IanMatthewHuff]

@Matelasse there is work being done to add native notebook UI support in VSCode. However experimental support for opening .ipynb files with that new UI is still a little ways over, we're actively working on it now.

[greazer]

@Matelasse, we will be publishing instructions in the near future on the python blog.