Note: this script is only for elementary beta 1 users: users of subsequent daily builds only need to run the gsettings command below to get the minimize icon to appear, since it is now included.
The file should be unzipped and then Add-Minimize.sh executed from within the extracted folder. The script will copy the new minimize icons into the appropriate directory, and the necessary xml file to modify the theme, and finally will implement your choice of gsettings command to add the minimize feature to your window.
After running the script, if you change your mind about the location of the button, you need to provide the appropriate gsettings command to change the gala button layout e.g.
gsettings set org.pantheon.desktop.gala.appearance \
Thanks go to Valpskott for providing the script and better minimize icons.