Added some info on the Apple2 PFS (and AppleCommander).

platform/apple2enh/README

@@ -2,10 +2,28 @@ The platform/apple2enh/ directory is used for targeting an Enhanced Apple //e
 (or compatible) computer. Most things are shared between the 6502-based targets
 so please consult cpu/6502/README for further details.
 
+
 The following Apple II Ethernet cards are supported:
+
 - Uther:   Use driver cs8900a.eth  with the address $C0x0 (x = 8 + slot number).
 - LANceGS: Use driver lan91c96.eth with the address $C0x0 (x = 8 + slot number).
 
+
 In most cases it is desirable to use an emulator for the development and testing
 of a Contiki application. AppleWin is especially well suited as it emulates the
-Uther Ethernet card in slot 3. It is available at http://applewin.berlios.de/.
+Uther Ethernet card in slot 3. It is available at http://applewin.berlios.de/.
+
+
+The 'disk' make goal requires AppleCommander 1.3.5 or later. It is available at
+http://applecommander.sourceforge.net/.
+
+
+The apple2enh target supports a PFS that requires much less RAM than the POSIX
+file system. However this benefit comes with the following restrictions:
+
+- Only one file may be open at the same time.
+- Only read operations are supported but no write operations.
+- The files must be located in the same directory the application is located in
+  (the ProDOS prefix may very well point to another directory).
+- The network MTU size must be set at least to 1265 (the default is 1500).
+- No network function may be called while a file is open.