HHH-18809 update Javadoc with this usage

Signed-off-by: Gavin King <gavin@hibernate.org>

hibernate-core/src/main/java/org/hibernate/annotations/Formula.java

@@ -32,6 +32,15 @@ import static java.lang.annotation.RetentionPolicy.RUNTIME;
  * Character middleInitial;
  * </pre>
  * <p>
+ * By default, the fields of an entity are not updated with the results of evaluating
+ * the formula after an {@code insert} or {@code update}. The {@link Generated @Generated}
+ * annotation may be used to specify that this should happen:
+ * <pre>
+ * &#64;Generated  // evaluate the formula after an insert
+ * &#64;Formula("sub_total * (1.0 + tax)")
+ * BigDecimal totalWithTax;
+ * </pre>
+ * <p>
  * For an entity with {@linkplain jakarta.persistence.SecondaryTable secondary tables},
  * a formula may involve columns of the primary table, or columns of any one of the
  * secondary tables. But it may not involve columns of more than one table.

hibernate-core/src/main/java/org/hibernate/annotations/Generated.java

@@ -31,11 +31,13 @@ import static org.hibernate.generator.EventType.INSERT;
  * <li>a mapped column has a default value defined in DDL, in which case
  *     {@code @Generated} is used in conjunction with {@link ColumnDefault},
  * <li>a {@linkplain #sql() SQL expression} is used to compute the value of
- *     a mapped column, or
+ *     a mapped column,
- * <li>when a custom SQL {@link SQLInsert insert} or {@link SQLUpdate update}
+ * <li>a custom SQL {@link SQLInsert insert} or {@link SQLUpdate update}
  *     statement specified by an entity assigns a value to the annotated
- *     property of the entity, or {@linkplain #writable() transforms} the
+ *     property of the entity, or {@linkplain #writable transforms} the
- *     value currently assigned to the annotated property.
+ *     value currently assigned to the annotated property, or
+ * <li>there is no mapped column, and the value of the field is determined
+ *     by evaluating a SQL {@link Formula}.
  * </ul>
  * <p>
  * On the other hand: