Flash instructions updated

[Christopher Beland]

Based on the recent conversations on this list, I have updated:

https://fedoraproject.org/wiki/Flash

If you use these instructions and they fail or you can otherwise tell
they are incorrect, please either fix them directly on the wiki or let
me know and I will fix them.

Hopefully this page can become a canonical, well-known resource so we
aren't answering this question a million times.

-B.