Add the basic developer's documentation for the Wasm port #12951

Job	Run time
Code style check / Code style check	5s
SonarCloud Analyzer / SonarCloud Analyzer	0s
CodeChecker / CodeChecker	31m 18s
IWYU / IWYU	3m 5s
MSVC / MSVC (SDL2 x86)	4m 10s
MSVC / MSVC (SDL2 x64)	4m 35s
Android / Android	9m 54s
CMake / CMake (Windows SDL2)	5m 29s
CMake / CMake (Linux SDL2)	2m 19s
Make / Make (Linux x86-64 SDL2 Release)	2m 59s
CMake / CMake (macOS SDL2)	1m 38s
Make / Make (Linux x86-64 SDL2 Debug)	3m 17s
CMake / CMake (macOS SDL2 App Bundle)	1m 45s
Make / Make (Linux ARM64 SDL2 Release)	4m 55s
Make / Make (Emscripten)	4m 2s
Make / Make (PS Vita)	9m 55s
Make / Make (Linux ARM64 SDL2 Debug)	5m 19s
Make / Make (macOS SDL2)	3m 44s
Make / Make (macOS SDL2 App Bundle)	2m 17s
Make / Make (Nintendo Switch)	3m 14s
	1h 44m 0s

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