Document usage of import libraries created by dlltool

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

doc/general.texi

@@ -1005,6 +1005,12 @@ libavutil/pixdesc.h you should have:
 extern __declspec(dllimport) const AVPixFmtDescriptor av_pix_fmt_descriptors[];
 @end example
 
+Note that using import libraries created by dlltool requires
+the linker optimization option to be set to
+"References: Keep Unreferenced Data (/OPT:NOREF)", otherwise
+the resulting binaries will fail during runtime. This isn't
+required when using import libraries generated by lib.exe.
+
 @subsection Cross compilation for Windows with Linux
 
 You must use the MinGW cross compilation tools available at