"Getting Started" content reorganization

[noah-severyn]

This has been on my list for awhile but I have finally gotten around to addressing some of it here in this PR. The main goal here was to focus on the 'Getting Started' section and to make a much more streamlined path through the documentation, with one single path to follow through the introduction, installation, and basics. Here's the highlights:

• Merged the 'start here' and 'overview of NAM' pages into one single, better formed introduction page
• Condensed down the 'Installation' page and reorganized it into two tabs for either first time installation or upgrading. I moved the troubleshooting section to its own page as it was getting quite hefty. I wanted to minimize the text on the page as it was a bit overwhelming, and only show users the part(s) that are relevant for their setup.
• Misc other small grammatical and styling changes to the Basics and FAQ pages; these remain mostly unchanged content-wise. One or two items were added to the FAQ.
• Added a little bit of content about the NAM lite; I'd like to expand this later but it's ok for now.

Sadly that means the Italian translations for these pages are now pretty out of date, but I'm not sure any other ways around that. Though I do have access to free monthly Azure AI Text Translation credits, so that's possibly worth discussing if anyone is interested.

Let me know your thoughts!