get contents and permalink from a specified page

To display content and permalink of About Us page you should use get_permalink() function by passing page id to it and instead of the_content_rss() function, you should directly echo $page->post_content by trimming content using wp_trim_words() function.

The changed code is as following.

<?php
    $page = get_page_by_title( 'About Us' );
    $content = apply_filters('the_content', $page->post_content); 

     echo wp_trim_words( $content, 100, '');
?>

<a href="https://wordpress.stackexchange.com/questions/110739/<?php  echo get_permalink( $page->ID ); ?>" title="Read the whole post" class="rm">Read More</a>