add comment explaining the use of now_or_never

Author: jakobhellermann

crates/bevy_render/src/render_resource/pipeline_cache.rs

@@ -135,6 +135,11 @@ impl ShaderCache {
                     .push_error_scope(wgpu::ErrorFilter::Validation);
                 let shader_module = render_device.create_shader_module(&module_descriptor);
                 let error = render_device.wgpu_device().pop_error_scope();
+
+                // `now_or_never` will return Some if the future is ready and None otherwise.
+                // On native platforms, wgpu will yield the error immediatly while on wasm it may take longer since the browser APIs are asynchronous.
+                // So to keep the complexity of the ShaderCache low, we will only catch this error early on native platforms,
+                // and on wasm the error will be handled by wgpu and crash the application.
                 if let Some(Some(wgpu::Error::Validation { description, .. })) =
                     futures_helper::now_or_never(error)
                 {