3-0 installation instructions update

- correct composer command line to  be consistent with cakephp/app repo.
- remove reference to old avdanced installation chapter.
- correct .htaccess content and location
- correct II7S XML file

I have no way to test the XML file on windows server so I just did the corrections that make sense to me. If you prefer, I oculd remove it from the PR and open an issue until someone could test it.
I propose to keep this line with [L] only has the .htaccess is like this out of the box and I can keep the QSA for the two "advanced" examples bellow. Does this makes sense ?