Administrative Items for move

[stevvooe]

Now that this repository has been moved to opencontainers, we'll need to update several administrative items. If there is anything missing, please edit this description or comment and I'll add it here. Once an item has a PR open, we can add it here and check it off when merged.

• Update travis CI build configuration (nothing to do here)
• Update project urls (README: update project urls for badges et al. #22)
• MAINTAINERS
  • Update maintainers with OCI project format (MAINTAINERS: update maintainers file #19)
  • Setup maintainers group (Clarify MAINTAINERS post OCI move #15)
  • PullApprove configuration (Add PullApprove config #16)
• Update files to have license header, per image-spec/runtime-spec (*: add LICENSE headers to Go files #28)
• Apply oci project template (*: Pull opencontainers/project-template #20)
• Update security statement to be in line with OCI procedures (README: update security email #27)

[caniszczyk]

Great to see this done, thanks @stevvooe