add extra cygwin packages code example

Example: add extra cygwin packages

# You can add extra packages using the cygwin installer that you can download
# from https://cygwin.com/ .
# A method that works from the command like in a way similar to well known
# 'apt-get' method is the script 'apt-cyg'.
# You can install it like this:
wget https://raw.githubusercontent.com/transcode-open/apt-cyg/master/apt-cyg
chmod +x apt-cyg
mv apt-cyg /usr/bin
# Example to use apt-cyg
apt-cyg install python3-devel