Tractor upgrades

Two short Markdown paragraphs providing an overview and key rules for Tractor Upgrades.

Paragraph 1: Tractor Upgrades offers a compact guide to the two-deck upgrades variant of Tractor, designed for four players. It covers deck setup, dealing, and the basic flow of a round.

Paragraph 2: Key rules highlighted include:

• Two 108-card decks
• Random card order
• Dealing to four players
• Calling the master and keeping other players blind until cards are revealed
• The first anti-bottom pile and its color-change rule
• Banker (zhuang) rotation after each round