bgpwtf/invoice: render SP/GTU codes on invoices

Change-Id: I2f47595c67ae0c945fa680b394cb7d5212cd389a
diff --git a/bgpwtf/invoice/templates/invoice_pl.html b/bgpwtf/invoice/templates/invoice_pl.html
index 15f5d08..b09086b 100644
--- a/bgpwtf/invoice/templates/invoice_pl.html
+++ b/bgpwtf/invoice/templates/invoice_pl.html
@@ -92,6 +92,9 @@
     -webkit-transform: rotate(-45deg);
     text-transform: uppercase;
 }
+div.symbols {
+    padding: 0 0 0.5rem 0.1rem;
+}
         </style>
     </head>
     <body>
@@ -154,6 +157,9 @@
             </div>
         </div>
         <div style="clear: both; height: 1em;"></div>
+        <div class="symbols">
+            <b>Oznaczenia</b>: {{ .Symbols }}
+        </div>
         <table class="items">
             <tr>
                 <th style="width: 60%;">Nazwa towaru lub usługi</th>