Update build_notes_windows.md

docs/build_notes_windows.md

@@ -165,9 +165,13 @@ Note that you might need to build DLL yourself for 64-bit systems
 using msys2 as 64-bit DLLs are not provided by the project.
 
 You can also install it through the MSYS2
+
+```bash
 pacman -S mingw-w64-i686-miniupnpc  
 and build with USE_UPNP key  
 make USE_UPNP=1  
+```
+
 It requires libminiupnpc.dll from /mingw32/bin  
 
 ### Creating Visual Studio project