Add mothers' day and fathers' day

Closes: #8

templates/index.html

@@ -19,6 +19,15 @@
       {{"{:.1f}".format(lockdown_days)}} days
       ({{"{:.2f}".format(lockdown_days / 7)}} weeks) so far</li> #}
     <li>The Economist: {{days(next_economist)}} (Thursday)</li>
+
+    <li>Mothers' day:
+      {{days(mothers_day)}}
+      {{mothers_day.strftime("%a, %d %b %Y")}}</li>
+
+    <li>Fathers' day:
+      {{days(fathers_day)}}
+      {{fathers_day.strftime("%a, %d %b %Y")}}</li>
+
     <li>UK bank holiday:
       {{days(bank_holiday["date"])}}
       {{bank_holiday["date"].strftime("%a, %d %b")}}