Minor change to README to remove closing the FileSystem from the example.

Since closing the FileSystem is not so important now that it can be GCed regardless.
Also adds a small reference to Windows-style file systems and a disclaimer about the
behavior's ability to exactly match that of any specific file system.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=67631673