Add Wordpress upgrade notice to plugins screen

plugin-update-notice.php

/**
 * Include the upgrade notice that will fire when 2.0.0 is released.
 * This must be added before version 2.0.0 is released. 
 *
 * @param array $plugin_data information about the plugin
 * @param array $r response from the server about the new version
 */
function your_update_notice( $plugin_data, $r ) {

	// Bail if the update notice is not relevant (new version is not yet 2.0 or we're already on 2.0)
	if ( version_compare( '2.0.0', $plugin_data['new_version'], '>' ) || version_compare( '2.0.0', $plugin_data['Version'], '<=' ) ) {
		return;
	}

	$update_notice = '</p><div class="wc_plugin_upgrade_notice">';

	// translators: placeholders are opening and closing tags. Leads to docs on version 2.0.0
	$update_notice .= sprintf( __( 'Warning! Version 2.0.0 is a major update and will break ALL THE THINGZ! Before updating, please test and update your custom templates with version 2.0.0 on a staging site. %sLearn more about the changes in version 2.0.0 &raquo;%s', 'your-plugin-text-domain' ), '<a href="https://docs.yoursite.com/document/major-frakking-update/">', '</a>' );
	
	$update_notice .= '</div><p class="dummy" style="display:none">';

	echo wp_kses_post( $update_notice );

}

add_action( 'in_plugin_update_message-your-plugin-folder/your-plugin-file.php', 'your_update_notice', 10, 2 );