Add link to hapax legomena article (fix #48)

application/templates/model.html

@@ -30,7 +30,7 @@ <h2>1. Corpus and Parameter Summary</h2>
       {{ table|safe }}
     {% endfor %}
     <br>
-    As you can see, your corpus is much smaller after cleaning. You {{ cleaning|safe }}. In addition so-called <i>hapax legomena</i> have been removed. In corpus linguistics, a hapax legomenon is a word that occurs only once within a context. So, if a word occurs only once in a document, it is very likely that the word is semantically insignificant – that is, not useful for the model.
+    As you can see, your corpus is much smaller after cleaning. You {{ cleaning|safe }}. In addition so-called <a href="https://en.wikipedia.org/wiki/Hapax_legomenon"><i>hapax legomena</i></a> have been removed. In corpus linguistics, a hapax legomenon is a word that occurs only once within a context. So, if a word occurs only once in a document, it is very likely that the word is semantically insignificant – that is, not useful for the model.
     <br>
     <br>
     <center>{{ corpus_boxplot_div|safe }}</center>