Improved the advanced app template documentation.

I'm just starting to use the template.  I'm sure I will have more feedback in a few weeks after some use of it.  This is mostly grammatical changes.

I did change the recommended composer installation command, as the composer website recommends using the `-sS` flags on `curl`.  The capital `S` from the curl manual:  "When used with -s it makes curl show an error message if it fails."

One important point of note, is the documentation says this:  
>  This application template also goes a bit further regarding features and provides essential database, signup and password restore out of the box.

Yet, it says nothing more than that about the signup, password restore, etc...