Update "Linux: Download Required Software" page

[AmarOk1412]

Hi @kendmaclean
I'm currently trying to do some stuff with Julius and I discovered the voxforge project (thx a lot).
When I read this page I ask myself some questions:

• This page is not up-to-date, how can I modify this page? I can't update the doc with an account.
• Finally I discover this repository, but it's not all of the website.

So, I think you can change at least 2 things on this page:

1. Log out and log back in to make your path change effective -> You should use "source ~/.bash_profile"
2. On Fedora, we use dnf instead of yum today.

Have a nice day,