Added README.md with build instructions for Windows.

Author: svenemtell

README.md

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+# Building SoX dynamic library (libsox-3.dll) on Windows
+
+libsox and its prerequisites libogg and libvorbis are built using autoconf in MinGW/MSYS.
+
+## 0. Make sure you have installed MinGW/MSYS
+Download and install from http://www.mingw.org.
+
+## 1. Build libogg
+1. Download libogg from https://xiph.org/downloads/. The lastest version as of this writing is 1.3.4.
+2. Open a `MinGW Shell` and to the libogg folder and run
+```
+./configure && make
+```
+
+## 2. Build libvorbis
+1. Download libvorbis from https://xiph.org/downloads/. The lastest version as of this writing is 1.3.6.
+2. Open a `MinGW Shell` and go to the libvorbis folder and run (change the paths for ogg-libraries and ogg-includes to suit your locations)
+```
+./configure --with-ogg-libraries=Z:\vmware-share\libogg-1.3.4\src\.libs --with-ogg-includes=Z:\vmware-share\libogg-1.3.4\include\ogg --disable-oggtest && make
+```
+
+## 3. Build libsox
+1. Open a `MinGW Shell` and standing in this folder run
+```
+./configure --without-magic --without-png --without-ladspa --without-opus --without-mad --without-libltdl --without-coreaudio --without-gsm --without-lpc10 --with-mpg123 --disable-static --enable-shared && make
+```
+2. The result can be found in `src/.libs/libsox-3.dll`.