add reference

bobjiang · bobjiang · commit 3ab80c1541bc · 2018-06-08T21:14:05.000+08:00
diff --git a/how-to-issue-erc875-token.md b/how-to-issue-erc875-token.md
@@ -97,3 +97,7 @@ You can redeem, sell, or transfer your own token like a ticket.
 
 Enjoy it!
 
+
+**Reference**
+
+[AlphaWallet ERC875 Sample](https://awallet.io/erc875-sample-1/)
