Update document with the new flippy mod doc; explain how Mac disks are broken.

README.md

@@ -89,7 +89,7 @@ people who've had it work).
 | [Brother 120kB](doc/disk-brother.md)     |  🦄   |        |                                     |
 | [Brother 240kB](doc/disk-brother.md)     |  🦄   |   🦄   |                                     |
 | [Brother FB-100](doc/disk-fb100.md)      |  🦖   |        | Tandy Model 100, Husky Hunter, knitting machines |
-| [Macintosh 800kB](doc/disk-macintosh.md) |  🦄   |        | and probably the 400kB too          |
+| [Macintosh 800kB](doc/disk-macintosh.md) |  🦖   |        | and probably the 400kB too          |
 | [TRS-80](doc/disk-trs80.md)              |  🦖   |        | a minor variation of the IBM scheme |
 {: .datatable }
 

doc/disk-macintosh.md

@@ -28,8 +28,16 @@ for example the Commodore 64 1541 drive, changed bitrate this way.
 But Macintosh disks used a constant bitrate and changed the speed that the
 disk spun instead to achieve the same effect...
 
-_Anyway_: FluxEngine will read them fine on a conventional drive. Because
-it's clever.
+_Anyway_: FluxEngine will read them fine on conventional drives.
+Because it's clever.
+
+**Big note.** Apparently --- and I'm still getting to the bottom of this ---
+some drives work and some don't. My drives produce about 90% good reads of
+known good disks. One rumour I've heard is that drives sometimes include
+filters which damage the signals at very particular intervals which Mac disks
+use, but frankly this seems unlikely; it could be a software issue at my end
+and I'm investigating. If you have any insight, please [get in
+touch](https://github.com/davidgiven/fluxengine/issues/new).
 
 Reading discs
 -------------

doc/faq.md

@@ -48,7 +48,7 @@ haven't had the chance to try it end-for-end. I really need a hard-sectored
 
 **Q.** Does it work with flippy disks?
 
-Uhhh... probably not.
+Uhhh... maybe?
 
 So the problem with flippy disks (5.25" single-sided disks which could be
 inserted upside down to read the second side) is the index hole. Trouble is,
@@ -79,16 +79,21 @@ the other. But a flippy disk has both sets of tracks in the same place,
 because they're both accessed using the side 0 head...
 
 The only real way round this is to modify a 5.25" drive. That's _seriously_
-not in FluxEngine's remit. Sorry.
+not in FluxEngine's remit, but I've had some [excellent documentation
+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).
 
-**Q.** Is this like KryoFlux / Catweasel / DiskFerret? Do you support KryoFlux
+**Q.** Is this like Supercard Pro / KryoFlux / Catweasel / DiskFerret? Do you
+*support KryoFlux
 stream files?
 
 **A.** It's very like all of these; the idea's old, and lots of people have
 tried it (you can get away with any sufficiently fast microcontroller and
 enough RAM). FluxEngine can read from KryoFlux stream files natively, and
-there's a tool which will let you convert at least one kind of Catweasel file
-to FluxEngine's native flux file format.
+there's a tool which will let you convert at least one kind of Catweasel
+files and Supercard Pro files to and from FluxEngine's native flux file
+format.
 
 **Q.** Can I use this to make exact copies of disks?