fixed formatting

README.md

@@ -2,8 +2,10 @@
 
 Usage: ./rpki-home.pl <rpki|routes|genbl|apply|all>
 
+```
   rpki  : download RPKI validator data
   routes: download RIPE RIS routing table dumps
   genbl : calculate the blacklist
   apply : swap ipsets
   all   : all of the above
+```