CRI Implementation metadata

[coderanger]

There is already a category for "container runtimes" which is great but is more generally scoped, it would be nice if there was some way to get a list specifically of CRI implementations, or runtimes that are CRI compatible. Not sure if this should be a new implements CRI: true field, or a category, or something else :) With the Dockershim deprecation, a lot of folks will want to see their options specifically re: CRI.