docs: Hint envvars needs to use the hint string, not the macro name

docs/README-wayland.md

@@ -12,7 +12,7 @@ encounter limitations or behavior that is different from other windowing systems
   DPI-aware to be automatically scaled by the window manager, which results in them being blurry. SDL can _attempt_ to
   scale these applications such that they will be output with a 1:1 pixel aspect, however this may be buggy, especially
   with odd-sized windows and/or scale factors that aren't quarter-increments (125%, 150%, etc...). To enable this, set
-  the environment variable `SDL_HINT_VIDEO_WAYLAND_SCALE_TO_DISPLAY=1`
+  the environment variable `SDL_VIDEO_WAYLAND_SCALE_TO_DISPLAY=1`
 
 ### Window decorations are missing, or the decorations look strange