docs: admin-guide: hw_random: update rng-tools website

rng-tools upstream moved to github. New upstream does not appear to
consider itself official website for hw_random. Drop that part.
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/ef52ace5008fa934084442149f64f5f9ddbba465.1704720105.git.baruch@tkos.co.il

Documentation/admin-guide/hw_random.rst

@@ -14,10 +14,9 @@ into that core.
 
 To make the most effective use of these mechanisms, you
 should download the support software as well.  Download the
-latest version of the "rng-tools" package from the
-hw_random driver's official Web site:
+latest version of the "rng-tools" package from:
 
-	http://sourceforge.net/projects/gkernel/
+	https://github.com/nhorman/rng-tools
 
 Those tools use /dev/hwrng to fill the kernel entropy pool,
 which is used internally and exported by the /dev/urandom and