Add link to SDBlockDevice.md

Add link now that Doxygen's fixed.

Author: Amanda Butler

docs/reference/api/storage/SDBlockDevice.md

@@ -64,7 +64,7 @@ The figure above shows the Mbed OS software component stack used for data storag
 
 ### SDBlockDevice class reference
 
-<!--- [![View code](https://www.mbed.com/embed/?type=library)](<Should be added after doxygen run>) --->
+[![View code](https://www.mbed.com/embed/?type=library)](http://os-doc-builder.test.mbed.com/docs/development/mbed-os-api-doxy/class_s_d_block_device.html)
 
 ### SDBlockDevice example application