Added a README file regarding WinRT support

To note, this file is currently formatted with CRLF line endings, rather than
LF, to allow the file to be viewed with Notepad.

build-scripts/updaterev.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+#
+# Generate a header file with the current source revision
+
+outdir=`pwd`
+cd `dirname $0`
+srcdir=..
+header=$outdir/include/SDL_revision.h
+
+rev=`sh showrev.sh 2>/dev/null`
+if [ "$rev" != "" -a "$rev" != "hg-0:baadf00d" ]; then
+    revnum=`echo $rev | sed 's,hg-\([0-9]*\).*,\1,'`
+    echo "#define SDL_REVISION \"$rev\"" >"$header.new"
+    echo "#define SDL_REVISION_NUMBER $revnum" >>"$header.new"
+    if diff $header $header.new >/dev/null 2>&1; then
+        rm "$header.new"
+    else
+        mv "$header.new" "$header"
+    fi
+fi