Improve the README text quality
Improve the README text quality

Stylistic edits, fixing some typos, making some sentences a little cleaner.
yisibl/autoprefixer,danielmorosan/autoprefixer,cemoulto/autoprefixer,aidenzou/autoprefixer,avanderhoorn/autoprefixer,iorikiir/autoprefixer,ocean90/autoprefixer,cgvarela/autoprefixer,NateBaldwinDesign/autoprefixer,postcss/autoprefixer,crobays/autoprefixer,dantman/autoprefixer,rzhw/autoprefixer