Currently, when you click [View All Fuel-ups] you also get all notes. They're listed alongside the fuel-ups by date. I'm not sure offhand what seeing the notes on a separate page would add. That's just my take, I like seeing them in context like that, but there might be a case for separating them.
And I'm not sure how we could add notes to the line graph. Each point on the graph is based on a calculated MPG. Since notes don't have an MPG, there's no place to position the note on the graph.