Adding notes are a great way to keep a track of changes you're making to your site and then correlating them to any performance changes you're seeing.
Notes are shown on your charts as a vertical line.
To manually add a note you can click on point on a chart and then select "Add Note". You can also go to your "Settings" and add or edit existing notes.
You can also use our Deploy API to let us know each time a deploy is pushed to production. As part of the API call you can add a note to track how deploys are affecting performance.