Remove all things from main

[jni]

As suggested by @neuromusic in this comment, this PR removes everything from the repo and clears the README to a barebones message pointing users to our contributing guide (soon to be a docs contributing guide).

[jni]

Here's the README btw, because navigating all the deleted files is horrible:

https://github.com/napari/napari.github.io/blob/021eed08ae477001846da8efe8298a8e907b59f2/README.md

[tlambert03]

thanks @codemonkey800!