docs: Grammar + spelling improvements
docs: Grammar + spelling improvements

I've just brushed up some bits of grammar and spelling to make the docs slightly more readable.
I think 'Csv' should be 'CSV' in writing (because it's an acronym) and `csv` in code (because that's convention), but I realise the author might have different taste to me so I left it out.
henriquebastos/python-decouple