Add helper function for creating a readable byte size string.

src/citra_qt/util/util.h

@@ -5,6 +5,10 @@
 #pragma once
 
 #include <QFont>
+#include <QString>
 
 /// Returns a QFont object appropriate to use as a monospace font for debugging widgets, etc.
 QFont GetMonospaceFont();
+
+/// Convert a size in bytes into a readable format (KiB, MiB, etc.)
+QString ReadableByteSize(qulonglong size);