added useful links section

added useful links section and research unix repository.

README.md

@@ -7,6 +7,11 @@ These are not capable of being compiled today with modern c compilers like gcc.
 
 You guys might be able to play around building this compilier with Aiju's pdp-11/unix emulator. I havent tried building this myself so I cant confirm it works, but I posted the link to his emulator for anybody wanting to hack around with it.
 
-Source: [https://www.bell-labs.com/usr/dmr/www/primevalC.html] [alt http://cm.bell-labs.co/who/dmr/primevalC.html]
+Source: [https://www.bell-labs.com/usr/dmr/www/primevalC.html] 
 
-PDP-11 Emulator[http://pdp11.aiju.de/]
+[alt-link http://cm.bell-labs.co/who/dmr/primevalC.html]
+
+**Useful Links
+
+PDP-11 Emulator: [http://pdp11.aiju.de/]
+Research Unix Repository: [https://www.tuhs.org/Archive/Distributions/Research/]