README: Add information on cross-compiling for Windows

README

@@ -17,6 +17,29 @@ Compile and Install:
   # make install
 
 
+Cross-Compile for Windows:
+
+  You'll want mingw-cross-env installed, with libX11 and mingw-catgets built.
+  A configure line that works is:
+  $ ./configure \
+        --prefix=/ \
+        --host=i686-pc-mingw32 \
+        --disable-imlib2 \
+        --disable-xmb \
+        --disable-slit \
+        --disable-remember \
+        --disable-toolbar \
+        --disable-fribidi \
+        --disable-nls \
+        --disable-xft \
+        LIBS="-lxcb -lXdmcp -lXau -lpthread -lws2_32"
+
+  Then, build and install with
+  $ make install DESTDIR=$(pwd)/stage
+
+  You can then copy the whole "stage" directory to a Windows machine and
+  run it on your choice of X server.
+
 Thanks:
 
   Blackbox team