Replace confusing "supplied time units" with "time-based units" (which are well defined by ChronoUnit)

      * The unit must have a {@linkplain TemporalUnit#getDuration() duration}
      * that divides into the length of a standard day without remainder.
- * This includes all supplied time units on {@link ChronoUnit} and
- * {@link ChronoUnit#DAYS DAYS}. Other ChronoUnits throw an exception.
+ * This includes all
+ * {@linkplain ChronoUnit#isTimeBased() time-based units on {@code ChronoUnit}}
+ * and {@link ChronoUnit#DAYS DAYS}. Other ChronoUnits throw an exception.

Remove redundant "the"

- * For example, the following will result in the exactly the same duration:
+ * For example, the following will result in exactly the same duration:

We should clarify that Duration.truncateTo will round TOWARDS ZERO.

      * For example, truncating with the {@link ChronoUnit#MINUTES MINUTES} unit will
- * round down to the nearest minute, setting the seconds and nanoseconds to zero.
+ * round down towards zero to the nearest minute, setting the seconds and
+ * nanoseconds to zero.

and a pile of whitespace fixes.