readme: remove broken php5-fpm instructions
readme: remove broken php5-fpm instructions

pagespeed/ngx_pagespeed,pagespeed/ngx_pagespeed,0x0mar/ngx_pagespeed,wanrui/ngx_pagespeed,digideskio/ngx_pagespeed,wanrui/ngx_pagespeed,digideskio/ngx_pagespeed,0x0mar/ngx_pagespeed