You need a validator on the workflow so that it checks the comment was filled in as you resolve. There isn't one built-in, but you can write or find one. I use the one in the Misc-Workflow-Extensions plugin - https://marketplace.atlassian.com/plugins/com.innovalog.jmwe.jira-misc-workflow-extensions
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.