Add Pagination to custom Wp_Query with Isotope filtering

Hi guys,

I have implemented Isotope in a Adaptive Flat Child theme. Isotope is working great but now all the pages shows the latest 20 posts.. (I have many blog posts, showing 20 on each page.

How can I add pagination to this custom loop? E.g. on page 2 I want posts 21-41 to show etc.

<?php $the_query = new WP_Query( 'posts_per_page=20'); //Check the WP_Query docs to see how you can limit which posts to display ?>

<?php if ( $the_query->have_posts() ) : ?>

    <div id="isotope-list">

    <?php while ( $the_query->have_posts() ) : $the_query->the_post(); 

	$termsArray = get_the_terms( $post->ID, "category" );  //Get thevterms for this particular item
	$termsString = ""; //initialize the string that will contain the terms
		foreach ( $termsArray as $term ) { // for each term
			$termsString .= $term->slug.' '; //create a string that has all the slugs
		}
	?> 

	<div class="<?php echo $termsString; ?> item">

							<article  <?php post_class('post-prev clearfix');?>>

								<?php adaptive_flat_thumbnail(480, 300); 

									the_post_thumbnail();
								?>											

								<h2 class="prev-title"><a href="<?php the_permalink() ?>"><?php the_title();?></a></h2>

								<div class="meta-tags">
								<?php	do_action( 'adaptive_flat_post_meta' );
								wp_link_pages();?>
								</div>	

								<?php adaptive_flat_excerpt() ?>

							</article>

	</div> <!-- end item -->
    <?php endwhile;  ?>
    </div> <!-- end isotope-list -->
<?php endif; ?>

Isotope is integrated in this way: https://www.aliciaramirez.com/2014/03/integrating-isotope-with-wordpress/

Appreciate all help