Add QuadSPI example

Author: deepikabhavnani

docs/api/drivers/QuadSPI.md

@@ -20,6 +20,10 @@ For more information, please review the related content.
 
 [![View code](https://www.mbed.com/embed/?type=library)](http://os-doc-builder.test.mbed.com/docs/development/mbed-os-api-doxy/classmbed_1_1_q_s_p_i.html)
 
+### QuadSPI example
+
+ [![View Example](https://www.mbed.com/embed/?url=https://github.com/ARMmbed/mbed-os-examples-docs_only/tree/master/QSPI)](https://github.com/ARMmbed/mbed-os-examples-docs_only/blob/master/QSPI/main.cpp)
+
 ### Related content
 
 - [QSPI flash block device](https://github.com/ARMmbed/qspif-blockdevice).