default Seq<T> append(Iterable<? extends T> other) {
        return concat(other);
    }
Concatenate two streams.
<p>
<pre><code>
// (1, 2, 3, 4, 5, 6)
Seq.of(1, 2, 3).append(Seq.of(4, 5, 6))
</code></pre>

@see #concat(Stream[])
jOOL-java-8/src/main/java/org/jooq/lambda/Seq.java