Added README and dependency list for mingw32-qt.

README.md

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+This repository contains toolchains usable for crosscompiling with CMake. They
+are meant to be used on ArchLinux, but they can also (with some directory
+structure modifications) work on other systems.
+
+How to use them?
+================
+
+Suppose you have sources which use CMake build system. Create new clean build
+directory, pick any toolchain and run cmake with your selected toolchain in it,
+e.g.:
+
+    mkdir build-win
+    cd build-win
+    cmake -DCMAKE_TOOLCHAIN_FILE=~/toolchains/archlinux/Qt4-mingw32.cmake ..
+
+Now you can compile (and install/package) the application as usual:
+
+    make -j3
+    make package
+    make me happy
+
+The result is application crosscompiled for given architecture and system (here
+it is Qt4 application for Windows).
+
+Dependencies for crosscompiling
+===============================
+
+Every toolchain file has listed dependecies, which are needed for successful
+crosscompilation. Packages are available either in official ArchLinux
+repositories, in AUR or, for more exotic architectures, in [my own repository](https://github.com/mosra/archlinux).

archlinux/Qt4-mingw32.cmake

@@ -1,3 +1,12 @@
+#
+# Toolchain for crosscompiling Qt4 application for Windows on ArchLinux.
+#
+# Minimal dependencies:
+#
+#     mingw32-gcc
+#     mingw32-qt
+#
+
 # Target system name
 SET(CMAKE_SYSTEM_NAME   Windows)