add readme.

README.MD

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+Host FST
+--------
+
+This is a file system translator (and driver) for compatible Apple IIgs
+emulators.  It depends on emulator support (but should not cause problems
+if run on real hardware or an unsupportive emulator).
+
+This FST exposes a shared folder from your native file system as a volume 
+within GS/OS.  (The volume will not be available from ProDOS 8). Reading 
+or writing a file on the :Host drive will read or write the file directly 
+on the native file system.  File Types, Finder Info, and Resource Forks 
+are supported.
+
+In general any software that works with the HFS FST should work with the 
+Host FST.
+