Clarify fee inclusion in revenue-over-time graph help text (#5785)

Updates the help text for the revenue-over-time graph to clarify how fees are
treated. When viewing a subevent, revenue excludes all fees (including
cancellation fees). When viewing the full event, revenue includes all fees,
including cancellation fees from cancelled orders.

src/pretix/plugins/statistics/templates/pretixplugins/statistics/index.html

@@ -45,10 +45,19 @@
                 {% endif %}
                 <p class="help-block">
                     <small>
+                        {% if request.GET.subevent %}
                             {% blocktrans trimmed %}
                                 Only fully paid orders are counted.
                                 Orders paid in multiple payments are shown with the date of their last payment.
+                                Revenue excludes all fees, including cancellation fees.
                             {% endblocktrans %}
+                        {% else %}
+                            {% blocktrans trimmed %}
+                                Only fully paid orders are counted.
+                                Orders paid in multiple payments are shown with the date of their last payment.
+                                Revenue includes all fees, including cancellation fees from cancelled orders.
+                            {% endblocktrans %}
+                        {% endif %}
                     </small>
                 </p>
             </div>