Fix reference to readme in visual studio project

tinyxml2/tinyxml2.vcxproj

@@ -151,7 +151,7 @@
     <ClInclude Include="..\tinyxml2.h" />
   </ItemGroup>
   <ItemGroup>
-    <None Include="..\readme.txt" />
+    <None Include="..\readme.md" />
   </ItemGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">

tinyxml2/tinyxml2.vcxproj.filters

@@ -20,7 +20,7 @@
     </ClInclude>
   </ItemGroup>
   <ItemGroup>
-    <None Include="..\readme.txt">
+    <None Include="..\readme.md">
       <Filter>Source Files</Filter>
     </None>
   </ItemGroup>