Add Window compatibility note to docs

HiddenServiceDirGroupReadable has no effect in Windows

doc/tor.1.txt

@@ -2082,6 +2082,7 @@ The following options are used to configure a hidden service.
     If this option is set to 1, allow the filesystem group to read the
     hidden service directory and hostname file. If the option is set to 0,
     only owner is able to read the hidden service directory. (Default: 0)
+    Has no effect on Windows.
 
 TESTING NETWORK OPTIONS
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