update backend notes

Backends.md

@@ -4,18 +4,38 @@ Human library includes pre-bundled `CPU`, `WASM` and `WebGL` backends, there is
 
 <br>
 
-## Notes
+## WebGL Backend
 
-- CPU backend usage is not recommended for performance reasons  
+WebGL backend usage is fastest on systems with modern GPU  
-  as TensorFlow implementation in JavaScript is by far the slowest
-- WebGL backend usage is fastest on systems with modern GPU  
 although startup speed is a bit slower
+
+## CPU Backend
+
+CPU backend usage is not recommended for performance reasons  
+as TensorFlow implementation in JavaScript is by far the slowest
+
+## WASM Backend
+
 - WASM backend has good resuts under specific conditions:
   - Enable WASM SIMD support in your browser  
     (CPU parallel processing instructions)
   - Reduce size of input image (e.g. webcam)  
     as WASM does not have optimized image extraction methods
 
+### Loading WASM Files
+
+WASM backend requires access to `wasm` files which are part of `@tensorflow/tfjs-backend-wasm` package and included in  
+`node_modules/@tensorflow/tfjs-backend-wasm/dist/*.wasm` (different WASM file is loaded depending on detected capabilities)  
+
+Also, to be able to load WASM files your web server, web server has to set appropriate HTTP headers:
+
+```text
+Cross-Origin-Opener-Policy: same-origin
+Cross-Origin-Embedder-Policy: require-corp
+```
+
+Or load WASM files from a CDN such as <https://www.jsdelivr.com/package/npm/@tensorflow/tfjs-backend-wasm?path=dist>
+
 ### How to enable WASM SIMD support
 
 Chrome:
@@ -37,11 +57,6 @@ Firefox:
 
 ## Known Issues
 
-- **WASM** backend without SIMD has limited processing capabilities before it causes issues  
+See <TODO.md>
-  To avoid issues, start `human` with most models disabled and if needed, enable them one by one as each initializes  
-  Typical errors messages are:  
-  `Uncaught (in promise) Error: undefined tfjs-backend-wasm.wasm` or  
-  `RuntimeError: memory access out of bounds in tfjs-backend-wasm.wasm`
-  - **NodeJS** backend is missing key operations and thus neither `Face` nor `Hand` models are currently supported
 
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