Update README.md

[freddy1020]

line 30: "this means that" maybe redundant line 31: "various different" -> "various" since "various different" may be redundant. line 65: Add a comma after "Beyond this." line 84: "a" -> "an"

document errors I revised README.md in several places to make it clearer, concise and easy to READ. I have completed the checklist.