doc: fix casing of GitHub handles in README lists
@linkgoron and @ErickWendel have upper-case letters in their GitHub handle, but the README lists them as all lowercase. If we're adding some automation, it's simpler to have it match.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
@linkgoron and @ErickWendel have upper-case letters in their GitHub handle, but the README lists them as all lowercase. If we're adding some automation, it's simpler to have it match.