Update Index.rst

Here, I have attempted to add a little more clarity for the newbie. I think the extra phrases and concepts and ideas, such as telling them that they will use the extension manager, so that they will feel safe to progress onto the next page.
Merge branch 'patch-8' of https://github.com/timotheonb/TYPO3CMS-Tutorial-Templating into timotheonb-patch-8
Changed phrasing a litle bit.
Merge branch 'timotheonb-patch-8' into latest