Tweaked the openSUSE build service links

~~This adds links to the openSUSE wiki with further information~~
* ~~https://en.opensuse.org/OpenRA~~
* ~~https://en.opensuse.org/Games~~

and avoids linking the download page twice. Also it may be confusing that you don't get a package, but another HTML site with instructions. I tried to mitigate that by renaming the button a bit.
Please remove "unstable" from before playtests here and below.  This was a deliberate change I made for all of the platforms when overhauling the download page because it gives a misleading impression of them.