How do i add a "more"-link/button to excerpts?

Hi, i’m using excerpts for my posts at http://www.losziehn.de to introduce them nicely at the home page and category/tags-pages. All good, but I would like to add some kind of “Read more…”-link or -button right after an excerpt.

During my research I found some introductions, eg. http://codex.wordpress.org/Excerpt or http://www.wpbeginner.com/wp-tutoria…ress-excerpts/ (last one shows how it should look like). But none of it worked. For example I put like suggested in that wordpress.org-codex following code in my index.php directly below <?php the_excerpt(); ?>:

<a href="<?php echo get_permalink(); ?>"> Read More...</a>

But a link or button doesn’ show up in the excerpts. What did I do wrong or does anyone have another idea to fix that problem, eg. via a plugin?

Thx in advance!