added dynamic field link to company, to display on admin if it has a shop_link

companies/models.py

@@ -57,3 +57,8 @@ class Company(models.Model):
     class Meta:
         verbose_name = "Compañía"
         verbose_name_plural = "Compañías"
+
+    def link(self):
+        return self.shop_link is not None
+
+    link.boolean = True