BUILD: Modified CMake ImageMagick detection logic to work with CMake 2.8.

Modified CMake ImageMagick detection logic to work with CMake 2.8.
diff --git a/cmake/README.txt b/cmake/README.txt
new file mode 100644
index 0000000..ddad8fa
--- /dev/null
+++ b/cmake/README.txt
@@ -0,0 +1,9 @@
+The following files are copied out of CMake 2.8.
+- FindImageMagick.cmake
+- FindPackageHandleStandardArgs.cmake
+- FindPackageMessage.cmake
+
+I have also copied the Copyright.txt file out of cmake and renamed it:
+- Copyright_cmake.txt
+
+All other files are created and/or maintained by either LunarG Inc or Valve Corporation.
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