docs: frame pace colours as headroom vs quota-exhaustion risk

Reword the README line and the draw_usage_bar comment so green and red
describe what they mean for the user — green is headroom to ramp up,
red is a trajectory to exhaust the quota before it resets — rather than
the bare "ahead of / behind pace".

README.md

@@ -60,7 +60,7 @@ Once running, it will appear in your taskbar and as one or more tray icons in th
 - Right-click the taskbar widget or tray icon for refresh, displayed models, update frequency, Start with Windows, reset position, language, updates, and exit
 - Left-click the tray icon to toggle the taskbar widget on or off
 - Enable `Start with Windows` from the right-click menu if you want it to launch automatically when you sign in
-- Under right-click `Settings` → `Show pace indicator`, pick a `Tick` or `Solid` style to mark where your usage should be for the time elapsed, coloured red when you are ahead of pace and green when you are behind; pick `Off` to turn it off
+- Under right-click `Settings` → `Show pace indicator`, pick a `Tick` or `Solid` style to mark where your usage should be for the time elapsed: green means you have headroom to ramp up, red means you are on a trajectory to exceed your quota before it resets (stop work or pay for extra usage); pick `Off` to turn it off
 
 ### Models
 

src/window.rs

@@ -3022,15 +3022,16 @@ fn draw_usage_bar(
         //           where pace says the user should be (red overage over the
         //           orange accent, green headroom over the grey track).
         //   tick  — a thick vertical bar at the expected-pace position.
-        // Red means actual usage is ahead of pace, green means behind it.
+        // Green means usage is behind pace — headroom to ramp up. Red means
+        // usage is ahead of pace — on a trajectory to exhaust the quota early.
         if let Some(pace) = pace_pct {
             let expected = pace.clamp(0.0, 100.0);
             let actual = percent_clamped;
             let _ = is_dark;
             let pace_color = if expected < actual {
-                Color::from_hex("#E53935") // red — ahead of pace
+                Color::from_hex("#E53935") // red — ahead of pace, may exhaust quota early
             } else {
-                Color::from_hex("#43A047") // green — behind pace
+                Color::from_hex("#43A047") // green — behind pace, headroom to ramp up
             };
 
             if pace_solid {