Add README for conformance report calculation #1180

Job	Run time
build_containers (apigee/registry-authz-server, ., containers/registry-authz-server/Dockerfile)	1m 8s
build_containers (apigee/registry-spec-renderer, containers/registry-spec-renderer, containers/re...	44s
build_containers (apigee/registry-prism-mock-server, containers/registry-mock-server/openapi, con...	1m 3s
build_containers (apigee/registry-graphql-mock-server, containers/registry-mock-server/graphql, c...	45s
build_containers (apigee/registry-linters, ., containers/registry-linters/Dockerfile)	1m 41s
build_containers (apigee/registry-protoc-gen-doc, containers/registry-protoc-gen-doc, containers/...	10s
	5m 31s

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