Document the extra index pulses.

doc/faq.md

@@ -84,6 +84,11 @@ contributed](Index_sensor_mod_FDD_1.1.pdf) on how to do this. I've never done
 it myself; if you try this and it works/doesn't work, as always, [get in
 touch](https://github.com/davidgiven/fluxengine/issues/new).
 
+Another option is to fake the index signal to the drive completely. The
+FluxEngine emits suitable pulses for a 300RPM drive on pin 3[0] and the
+equivalent pulses for a 360RPM drive on pin 3[1]. Disclaimer: I have never used
+these.
+
 **Q.** Is this like Supercard Pro / KryoFlux / Catweasel / DiskFerret? Do you
 *support KryoFlux
 stream files?

doc/using.md

@@ -64,6 +64,16 @@ In order to do anything useful, you have to plug it in to a floppy disk drive (o
 
   9. Profit!
 
+## Bonus hardware features
+
+For advanced users, the board has a few extra signals which are useful for special purposes.
+
+  - Pin 3[0] produces short pulses every 200ms. This is useful for spoofing
+    index signals to 300 RPM drives; for example, to read flippy disks.
+
+  - Pin 3[1] is the same, but produces the pulses every 166ms; this works with
+    360 RPM drives.
+
 ## The programs
 
 I'm sorry to say that the client program is very badly documented --- it's