Add information above a custom post type listing of all posts page

functions.php

function wpa_admin_notice() {
    $screen = get_current_screen();
    if( 'your_post_type' == $screen->post_type
        && 'edit' == $screen->base ){
        ?>
        <div class="updated">
            <p>Here is some text</p>
        </div>
        <?php
    }
}
add_action( 'admin_notices', 'wpa_admin_notice' );

## Change your_post_type to whatever your custom post type slug is. 
## Also see get_current_screen on https://codex.wordpress.org/Function_Reference/get_current_screen  for more info on that function.