Improve WebGPU unstable flags docs (#10163)

# Objective

- Fixes #9382

## Solution

- Added a few extra notes in regards to WebGPU experimental state and
the need of enabling unstable APIs through certain attribute flags in
`cargo_features.md` and the examples `README.md` files.

Cargo.toml

@@ -241,7 +241,7 @@ shader_format_glsl = ["bevy_internal/shader_format_glsl"]
 # Enable support for shaders in SPIR-V
 shader_format_spirv = ["bevy_internal/shader_format_spirv"]
 
-# Enable some limitations to be able to use WebGL2. If not enabled, it will default to WebGPU in Wasm
+# Enable some limitations to be able to use WebGL2. If not enabled, it will default to WebGPU in Wasm. Please refer to the [WebGL2 and WebGPU](https://github.com/bevyengine/bevy/tree/latest/examples#webgl2-and-webgpu) section of the examples README for more information on how to run Wasm builds with WebGPU.
 webgl2 = ["bevy_internal/webgl"]
 
 # Enables watching the filesystem for Bevy Asset hot-reloading

docs-template/EXAMPLE_README.md.tpl

@@ -240,6 +240,14 @@ Bevy support for WebGPU is being worked on, but is currently experimental.
 
 To build for WebGPU, you'll need to disable default features and add all those you need, making sure to omit the `webgl2` feature.
 
+WebGPU depends on unstable APIs so you will also need to pass the `web_sys_unstable_apis` flag to your builds. For example:
+
+```sh
+RUSTFLAGS=--cfg=web_sys_unstable_apis cargo build ...
+```
+
+Check `wasm-bindgen` [docs on Unstable APIs](https://rustwasm.github.io/wasm-bindgen/web-sys/unstable-apis.html) for more details.
+
 Bevy has an helper to build its examples:
 
 - Build for WebGL2: `cargo run -p build-wasm-example -- --api webgl2 load_gltf`

docs/cargo_features.md

@@ -34,7 +34,7 @@ The default feature set enables most of the expected features of a game engine,
 |png|PNG image format support|
 |tonemapping_luts|Include tonemapping Look Up Tables KTX2 files|
 |vorbis|OGG/VORBIS audio format support|
-|webgl2|Enable some limitations to be able to use WebGL2. If not enabled, it will default to WebGPU in Wasm|
+|webgl2|Enable some limitations to be able to use WebGL2. If not enabled, it will default to WebGPU in Wasm. Please refer to the [WebGL2 and WebGPU](https://github.com/bevyengine/bevy/tree/latest/examples#webgl2-and-webgpu) section of the examples README for more information on how to run Wasm builds with WebGPU.|
 |x11|X11 display server support|
 |zstd|For KTX2 supercompression|
 

examples/README.md

@@ -544,6 +544,14 @@ Bevy support for WebGPU is being worked on, but is currently experimental.
 
 To build for WebGPU, you'll need to disable default features and add all those you need, making sure to omit the `webgl2` feature.
 
+WebGPU depends on unstable APIs so you will also need to pass the `web_sys_unstable_apis` flag to your builds. For example:
+
+```sh
+RUSTFLAGS=--cfg=web_sys_unstable_apis cargo build ...
+```
+
+Check `wasm-bindgen` [docs on Unstable APIs](https://rustwasm.github.io/wasm-bindgen/web-sys/unstable-apis.html) for more details.
+
 Bevy has an helper to build its examples:
 
 - Build for WebGL2: `cargo run -p build-wasm-example -- --api webgl2 load_gltf`