fixed broken link

Author: alcueca

developers/addresses/README.md

@@ -3,5 +3,5 @@
 All contract addresses and identifiers can be obtained through the "Download" button on the lower right corner of the application.
 
 <figure class="image" align = "center">
-  <img src="assets/png.png" alt="download button" title="download addresses and identifiers">
+  <img src="../../assets/addresses.png" alt="download button" title="download addresses and identifiers">
 </figure>