Update README.md: add "pacman -Syu" for Windows build

README.md

@@ -231,8 +231,10 @@ that case, but I haven't tested doing it like that. Sorry. Get a better OS...)
 
 4. Install the dependencies *(5-10 minutes)*  
    Once the shell opens, we need to install the dependencies for building
-   Purr Data. Issue the following command:
+   Purr Data. Issue the following two commands:
 
+        pacman -Syu
+        
         pacman -S autoconf automake git libtool \
           make mingw-w64-i686-dlfcn mingw-w64-i686-fftw \
           mingw-w64-i686-fluidsynth \