Added more docs.

doc.go

@@ -2,4 +2,18 @@
 // Author: jacobsa@google.com (Aaron Jacobs)
 
 // Package fuse enables writing and mounting user-space file systems.
+//
+// The primary elements of interest are:
+//
+//  *  The FileSystem interface, which defines the methods a file system must
+//     implement.
+//
+//  *  NotImplementedFileSystem, which may be embedded to obtain default
+//     implementations for all methods that are not of interest to a particular
+//     file system.
+//
+//  *  Mount, a function that allows for mounting a file system.
+//
+// In order to use this package to mount file systems on OS X, the system must
+// have FUSE for OS X installed: http://osxfuse.github.io/
 package fuse