Update container.md

[scoheb]

Update to use valid JSON. Otherwise, you'll see errors such as:

error: trailing comma at line 7 column 5

Thank you for contributing to rpm-ostree.

If you are adding functionality to tree composes, please add
a corresponding test to the compose-test suite. Similarly,
if adding a client-facing feature, consider the vmcheck
suite. Regressions fixes are also great candidates for new
tests.

If you're not sure where or how to add tests, don't hesitate
to ask for help from the maintainers.

Cheers!

[openshift-ci]

Hi @scoheb. Thanks for your PR.

I'm waiting for a coreos member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.