Updated Fedora Linux in README.md

[hegjon]

SILE is now included in Fedora Linux

[alerque]

I haven't reviewed my own work yet, but I'll dedup whatever I had in #1936 with this when I merge...

Thanks again for the work on packaging. I'll try to help out with the Rusty bump for v0.15 when I get a chance too.

[hegjon]

Ah, I forgot #1936