Review the installation/configuration.php-dist

See: https://github.com/joomla/joomla-cms/issues/4498

This is a review of the installation/configuration.php-dist file. I have add some comments move the default dbtype to mysqli and outcommend the root_user (<-- or is this realy needed?)

I don't know if this need any testing but it can be tested is the following:

1. download a clean staging
2. extract
3. move this file to the joomla root
4. change the needed settings
5. install the database manualy
6. make sure all works as if you use the installer.

Thanks @robations for pointing it out.
i assume you added the word full to show it should be http://www.example.com not just www.example.com
If that is correct then you should write a better string to say that