tweak dependency section

README.md

@@ -28,9 +28,17 @@ Key features:
 
 # System Requirements
 
-- A graphics card with vulkan support
+- Screen, keyboard, mouse
+- Operating System: Linux, Windows, MacOS
+- Ideally, a graphics card with vulkan support
 
-Workaround if you don't have a vulkan GPU: Enable the OpenGL rendering backend by setting the `WGPU_BACKEND` environment variable to `gl`, e.g. by running `WGPU_BACKEND=gl cargo run` or `WGPU_BACKEND=gl ./outfly`. Note that this has considerably slower performance and occasional visual glitches.
+If your GPU does not support vulkan, try rendering with OpenGL by setting the environment variable `WGPU_BACKEND` to `gl`, like:
+
+```
+WGPU_BACKEND=gl ./outfly
+or
+WGPU_BACKEND=gl cargo run
+```
 
 # Building
 ## On Linux