Need to update "Prerequisites" section documentation

[nicosocoro]

Considerations

• I'm using GStreamer mingw version 1.18.2. Not version 1.16.2 as indicated in the documentation.

Issue description

In README's Prerequisites section (working on Windows), it states we need to add two new values to PATH environment variable (EV):

• %GSTREAMER_1_0_ROOT_X86_64%\bin
• %GSTREAMER_1_0_ROOT_X86_64%\lib\gstreamer-1.0

However, when we install the GStreamer mingw version, it creates the GSTREAMER_1_0_ROOT_MINGW_X86_64 EV (notice the extra MINGW between ROOT and X86_64).

At first, I got an error related to not being able to find gstreamer-1.0-0.dll (similar as reported in Issue#1: You are missing gstreamer-1.0-0.dll). Although, adding MINGW made it work out.

To sum up, the two above values should be, respectively, updated to:

• %GSTREAMER_1_0_ROOT_MINGW_X86_64%\bin
• %GSTREAMER_1_0_ROOT_MINGW_X86_64%\lib\gstreamer-1.0

[MCREAPER-dotcom]

As i understand MINGW can avoided if you just use:
GLib.GType.Register(Gst.Element.GType, typeof(Gst.Element));
GLib.GType.Register(Gst.Pipeline.GType, typeof(Gst.Pipeline));
when innit you progect.

I won't say for sure, but it helped me compile on MSVC