Remove pdiff from README
Remove pdiff from README

Test Plan: Crossed fingers.

Auditors: emily

Khan/KaTeX,franciscop/KaTeX,spicyj/KaTeX,kwangkim/katex-npm-0.7.0-pre,crepererum/KaTeX,Khan/KaTeX,xymostech/KaTeX,zhanghuiguoanlige/KaTeX,kevinbarabash/KaTeX,kwangkim/KaTeX,twitwi/KaTeX,saschatimme/KaTeX,xymostech/KaTeX,gagern/KaTeX,azotova/KaTeX,frankandrobot/KaTeX,gagern/KaTeX,spicyj/KaTeX,franciscop/KaTeX,mcanthony/KaTeX,saschatimme/KaTeX,kwangkim/katex-npm-0.7.0-pre,frankandrobot/KaTeX,kwangkim/katex-npm-0.7.0-pre,zhanghuiguoanlige/KaTeX,zhanghuiguoanlige/KaTeX,JetStarBlues/KaTeX,gagern/KaTeX,JetStarBlues/KaTeX,azotova/KaTeX,kevinbarabash/KaTeX,kwangkim/KaTeX,kwangkim/katex-npm-0.7.0-pre,twitwi/KaTeX,JetStarBlues/KaTeX,franciscop/KaTeX,kwangkim/KaTeX,azotova/KaTeX,saschatimme/KaTeX,saschatimme/KaTeX,frankandrobot/KaTeX,azotova/KaTeX,crepererum/KaTeX,spicyj/KaTeX,gagern/KaTeX,Khan/KaTeX,spicyj/KaTeX,twitwi/KaTeX,mcanthony/KaTeX,azotova/KaTeX,crepererum/KaTeX,xymostech/KaTeX,kwangkim/KaTeX,frankandrobot/KaTeX,xymostech/KaTeX,mcanthony/KaTeX,frankandrobot/KaTeX,JetStarBlues/KaTeX,gagern/KaTeX,twitwi/KaTeX,mcanthony/KaTeX,mcanthony/KaTeX,kevinbarabash/KaTeX,kevinbarabash/KaTeX,kevinbarabash/KaTeX,JetStarBlues/KaTeX,kwangkim/KaTeX,saschatimme/KaTeX,xymostech/KaTeX,franciscop/KaTeX,crepererum/KaTeX,franciscop/KaTeX,twitwi/KaTeX,crepererum/KaTeX,kwangkim/katex-npm-0.7.0-pre,zhanghuiguoanlige/KaTeX,zhanghuiguoanlige/KaTeX,spicyj/KaTeX