[docs] Add missing JavaDocs (#6125)

wpimath/src/main/java/edu/wpi/first/math/InterpolatingMatrixTreeMap.java

@@ -9,6 +9,10 @@ import java.util.TreeMap;
 /**
  * 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.
+ *
+ * @param <K> Key type.
+ * @param <R> Number of matrix rows.
+ * @param <C> Number of matrix columns.
  */
 public class InterpolatingMatrixTreeMap<K extends Number, R extends Num, C extends Num> {
   private final TreeMap<K, Matrix<R, C>> m_map = new TreeMap<>();