[web] Update README with live ISO hints

[nagu165]

• Added extra information regarding the download procedure for Agama ISO files.
• Gave an overview of how to run Agama using the virtual machine

[ancorgs]

First of all, thanks a lot for the contribution. It's really nice that you want to add some clarifications to avoid newcomers confusion. But...

In its current form, this pull request adds quite some text with three points in which (according to previous comments from me and others):

• The first point contains a direct link that can lead to errors
• The second one is redundant with the previous paragraph
• The third one corresponds to a different topic

I think the same goal could be achieved with a less intrusive change. Something like this:

 You can download them from the [openSUSE Build
 Service](https://download.opensuse.org/repositories/systemsmanagement:/Agama:/Devel/images/iso/).
+Make sure to download the correct ISO file according to your system system architecture (eg.
+you would need to choose an file including `x86_64` if you use an Intel or AMD 64-bit processor)
+and according to the system you want to install (openSUSE vs ALP).

Writing a good README is much harder than it looks (there is a hard balance about what to include and what not). And maintaining it up to date is also very important (says a lot about the health of a project). So thank you sincerely for taking care and sorry for being a bit nitpicking. ;-)

[dgdavid]

@nagu165

Thank you a lot for this contribution, already merged in master branch. Hope it helps people to choose the right ISO.

Thanks also to my @openSUSE/yast team colleagues for given their feedback here. Much appreciated.