[dpdk-dev] MinGW guide

[Thomas Monjalon]

The Windows user guide is referencing a general link to download MinGW:
	http://mingw-w64.org/doku.php/download
For those who want to install MinGW on Windows, I thing it is simpler
to give this more direct link:
	http://mingw-w64.org/doku.php/download/mingw-builds
It avoids hesitating between different bundles (Cygwin, Msys2, Win-Builds, etc).

Then when installing mingw-w64-install.exe, a choice must be done
between threads POSIX or Win32.
If I understand well, POSIX must be chosen?
If it is important, it should be documented in my opinion.