[wpimath] Document example usage for InterpolatingDoubleTreeMap (NFC) (#6456)

wpimath/src/main/java/edu/wpi/first/math/interpolation/InterpolatingDoubleTreeMap.java

@@ -9,6 +9,17 @@ import java.util.Map;
 /**
  * Interpolating Tree Maps are used to get values at points that are not defined by making a guess
  * from points that are defined. This uses linear interpolation.
+ *
+ * <p>Example of use:
+ *
+ * <pre><code>
+ * InterpolatingDoubleTreeMap table = new InterpolatingDoubleTreeMap();
+ * table.put(0.0, 0.0);
+ * table.put(1.0, 10.0);
+ * table.put(2.0, 30.0);
+ * // ...
+ * double result = table.get(1.5); // Returns 20.0
+ * </code></pre>
  */
 public class InterpolatingDoubleTreeMap extends InterpolatingTreeMap<Double, Double> {
   /** Default constructor. */