We at Triggre strongly believe the application you make is self-explanatory. Also, our experience is that when you add comments to a User flow or other object it’s hard to keep it up to date. This will result in a remarks which doesn’t represent the logic anymore. That’s the reason why we don’t support adding comments and remarks to User flows and other objects.
In case you absolutely desire to create remarks you can also create an application (using Triggre for instance) where you can write down the User flow and the remarks you want to add to it.