How to Add Read More Code in Theme Function

Hi

From last 2 weeks im trying to add a feature as 250 words of post on page appear and rest of the article access by Read More Links

I have tried Tags and many tutorial but its seems my selected theme is not allowing or has bug in it. Alot of search I have found the following code which need to be add in function.php

<?php

add_filter( 'the_content_more_link', 'my_more_link', 10, 2 );

function my_more_link( $more_link, $more_link_text ) {
	return str_replace( $more_link_text, 'Continue reading &rarr;', $more_link );
}

?>

Taken from

https://justintadlock.com/archives/2009/07/01/how-to-filter-a-wordpress-themes-more-link-text

Here is my theme function Code. Please tell me how to adjust above code into my function.php file.

<?php

/**

 * Coded by misbah ([email protected])

 */

if ( function_exists('register_sidebar') ) {

	register_sidebar(array(

		'name' => 'Primary Sidebar',

		'before_widget' => '<li id="%1$s" class="widget">',

		'after_widget' => '</li>',

		'before_title' => '<h4 class="widget-title">',

		'after_title' => '</h4>',

	));

	register_sidebar(array(

		'name' => 'Secondary Sidebar',

		'before_widget' => '<li id="%1$s" class="widget">',

		'after_widget' => '</li>',

		'before_title' => '<h4 class="widget-title">',

		'after_title' => '</h4>',

	));

}

//Check for widgets in widget-ready areas https://www.ads-software.com/support/topic/190184?replies=7#post-808787

//Thanks to Chaos Kaizer https://blog.kaizeku.com/

function is_sidebar_active( $index = 1){

	$sidebars	= wp_get_sidebars_widgets();

	$key		= (string) 'sidebar-'.$index;

	return (isset($sidebars[$key]));

}

include(TEMPLATEPATH.'/includes/template-options.php');

include(TEMPLATEPATH.'/includes/plugins.php');

/*

add_action('widgets_init', 'remove_default_widgets', 0);

function remove_default_widgets() {

	if (function_exists('unregister_sidebar_widget')) {

		unregister_sidebar_widget('Search');

	}

}

include(TEMPLATEPATH.'/includes/widgets.php');

/**/

Thanks