Created Bulding for Windows (MSYS) (markdown)

Bulding-for-Windows-(MSYS).md

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+Get install file `msys2-$ARCH-*.exe` from `https://msys2.github.io`
+
+Where $ARCH is `i686` or `x86_64` (matching your system).
+
+- Open MSYS2 Shell (from Start menu).
+- Install all prerequisites:
+
+        export ARCH='i686'     # or 'x86_64'
+        export MINGW='mingw32' # or 'mingw64'
+        pacman -S mingw-w64-$ARCH-boost mingw-w64-$ARCH-openssl mingw-w64-$ARCH-gcc git make
+
+- Build gostcoin
+        mkdir -p /c/dev/gostcoin
+        cd /c/dev/gostcoin
+        git clone https://github.com/GOSTSec/gostcoin.git
+        # we need compiler on PATH which is usually heavily cluttered on Windows
+        export PATH=/$MINGW/bin:/usr/bin
+        cd gostcoin/i2psam
+        make -f makefile.mingw
+        cd ../src
+        make -f makefile.mingw