README: what the unlocked frame rate allows

The features list said the unlocked frame rate went "up to 120 FPS". In
0.7 it goes up to 480 FPS, the most the game's loading screens take, and
120 is the most the game's movement is sure to keep up with (the
launcher warns above it). The line now says so, and that the in-game
menu changes the frame rate while playing.

README.md

@@ -28,7 +28,8 @@ seamless co-op, the Steam Deck, and what to do when something goes wrong.
   **local co-op** (split screen), 2 to 4 players on one PC, each with their own controller.
 - **In-game map** (Hunter's Atlas): a fullscreen map with where you are, lamps and items, and fast
   travel to the lamps you've found.
-- **Frame rate unlocked** (up to 120 FPS) or capped at **30, 60 or 90**. Resolutions from
+- **Frame rate unlocked** (up to 120 FPS recommended; the game's movement can break above it)
+  or capped at **30, 60 or 90**, and changed while you play from the in-game menu. Resolutions from
   **720p to 4K**, and any **aspect ratio** (4:3 to 32:9 ultrawide, [how](docs/TROUBLESHOOTING.md#the-picture-is-stretched-on-an-ultrawide-screen)).
 - **Upscaling:** AMD **FSR 3.1** and **FSR 4**, NVIDIA **DLSS** (GeForce RTX) and TAA, and
   **frame generation** (FSR 3.1, or DLSS on GeForce RTX 40 and newer).