Update modules/ROOT/pages/packagekit-not-found.adoc
    
    Fixed some grammatical issues. About half of the content didn't copy over from the wiki, so I filled the rest in. Note: "this video" link under the subheader "What is bad about patented formats?" leads to an website which seems to have security issues. There is no SSL certificate for that link and my browser prompts me with a warning. I also removed other broken links. The suggestion to use Ogg Vorbis might be outdated, as I tried to visit the site and didn't get a response. I kept the link and content, however, because I'm not expert in this subject and have no alternative to offer.