Copy edits to the Getting started doc (#4962)
Copy edits to the Getting started doc (#4962)

* Another pass at the getting started doc

Sentence casing titles.
Making the first few paragraphs less wordy.
Restructured the contents of the Javascript section.

* Make minor grammatical fixes.

* Replace "we" with "you" to keep consistency for reader.

material-components/material-components-web,pgbross/material-components-web,pgbross/material-components-web,Yizhachok/material-components-web,anton-kachurin/material-components-web,material-components/material-components-web,material-components/material-components-web,anton-kachurin/material-components-web,Yizhachok/material-components-web