replace tokens removed by 3fc56dc. updated name footer.foo to something more descriptive

_includes/footer.html

@@ -2,7 +2,7 @@
 
   <hr class="footer-divider" />
 
-  <h3 id="participate">{% t footer.foo %}</h3>
+  <h3 id="participate">{% t footer.spread_the_word %}</h3>
 
   <div class="row mb-4">
     <div class="col-12 col-md-6 d-flex justify-content-between">