Add wasm build instructions to documentation #1224

Job	Run time
emscripten_wasm (ubu24, ubuntu-24.04, 3.1.45, bash)	3m 23s
build (ubu24, ubuntu-24.04, bash)	1m 18s
emscripten_wasm (osx13-x86, macos-13, 3.1.45, bash)	4m 45s
build (ubu24-analyzers, ubuntu-24.04, true, -DCMAKE_BUILD_TYPE=Debug, bash)	2m 55s
emscripten_wasm (osx14-arm, macos-14, 3.1.45, bash)	2m 51s
build (osx13-x86, macos-13, bash)	3m 41s
build (osx14-arm, macos-14, bash)	1m 27s
emscripten_wasm (osx15-arm, macos-15, 3.1.45, bash)	3m 0s
build (osx15-arm, macos-15, bash)	1m 24s
build (Windows22, windows-2022, cmd.exe)	2m 31s
	27m 15s

Provide feedback