Add SECURITY.md and security disclosure process

[caniszczyk]

[DARK-art108]

Can I work on this? @ytsarev

[ytsarev]

@DARK-art108 sure thing, that would be very cool! :)

[DARK-art108]

What all things needed to be added in Security.md @ytsarev !

[ytsarev]

@DARK-art108 well, figuring it out is the part of the job here I guess :)

High level, I think we need to go through examples like https://github.com/kubernetes/examples/blob/master/SECURITY.md and create something simple for k8gb