README: FAQ about scrypt and difficulty

README

@@ -712,6 +712,12 @@ Then logout and back in again
 Q: Can I mine scrypt with FPGAs or ASICs?
 A: No.
 
+Q: Why does BFGMiner show difficulty 0 when mining scrypt?
+A: BFGMiner consistently uses pdiff measurement for difficulty everywhere,
+rather than other measurements that may exist. For scrypt, pdiff 1 is very
+difficult, and higher get exponentially harder. It is unlikely you will want to
+use pdiff 1+ with scrypt until you have FPGAs and/or ASICs for it.
+
 Q: What is stratum and how do I use it?
 A: Stratum is a protocol designed to reduce resources for mining pools at the
 cost of keeping the miner in the dark and blindly transferring his mining