(since 2.5)
To enable "read more" links after your post excerpts, create/edit component nm-init and insert this (enclosed between <?php and ?> tags):
nm_set_option('excerpt','readmore');
Or if you want the "read more" always, even if the post content is shorter than the maximum excerpt length:
nm_set_option('excerpt','forcereadmore');
You can change the default "read more" text. Example:
nm_set_text('READ_MORE', 'Continue reading');