- added notes on how to build with emscripten

.emscripten/notes.md

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+# Emscripten info on how to build
+
+1. install VSExtForEmscripten for VS 2019
+2. with chocolatey - `choco install emsdk`
+
+#### Where chocolatey places SDK on windows:
+`\AppData\Local\emsdk\upstream\emscripten`
+
+## Building
+
+- switch optimization to O3 (Full optimization)
+
+- remove `/SAFESEH:NO` everywhere (if using VSExtForEmscripten)
+
+- remove Windows defines if copied from Win32 configuration
+
+- disable warnings: 
+c++11-narrowing;constant-conversion;writable-strings;unused-value;switch;shift-op-parentheses;parentheses;format
+
+add Clang parameters (Psy-X, REDRIVER2): 
+`-s USE_SDL=2 -s FULL_ES2=1 -s USE_WEBGL2=1 -s ASYNCIFY=1 -s ALLOW_MEMORY_GROWTH=1`
+
+add linker parameters (REDRIVER2): 
+`-s TOTAL_MEMORY=33554432 -s USE_SDL=2 -s FULL_ES2=1 -s USE_WEBGL2=1 -s ASYNCIFY=1 -s ALLOW_MEMORY_GROWTH=1 --preload-file ../data@/`
+