Adds plaintext code to emails

bookwyrm/templates/email/confirm/text_content.html

@@ -7,5 +7,8 @@ One last step before you join {{ site_name }}! Please confirm your email address
 
 {{ confirmation_link }}
 
+{% blocktrans trimmed %}
+Or enter the code "{{ confirmation_code }}" at login.
+{% endblocktrans %}
 
 {% endblock %}