IOService: clarify javadoc

The IOService is high-level; the DataHandleService is low-level.

Author: ctrueden

src/main/java/org/scijava/io/IOService.java

@@ -37,9 +37,11 @@
 import org.scijava.service.SciJavaService;
 
 /**
- * Interface for data I/O operations: opening and saving data.
+ * Interface for high-level data I/O: opening and saving data.
  * 
  * @author Curtis Rueden
+ * @see DataHandleService
+ * @see Location
  */
 public interface IOService extends HandlerService<String, IOPlugin<?>>,
 	SciJavaService