Add note that the .net bindings are broken with MSVC.
When building using MSVC, meson decides to change the name of the .dll files to be windows style, so A.dll instead of libA.dll. gst-sharp currently hardcodes to libgst*.dll so it doesn't work with these builds. Let's note it on the website as I guess the type of people who use .NET are also the type of people who use MSVC & pre-built binaries.