Add content to porting_reqs.md

Add DAPLink content back in.

Author: Amanda Butler

docs/porting/porting_full_process/porting_reqs.md

@@ -4,6 +4,7 @@
 
 Porting Mbed OS requires the following hardware:
 
+- A development PC. You can port targets, connectivity and storage on Windows, macOS or Linux. However, due to limitations in some development tools that Mbed OS uses, you need a Windows PC for DAPLink/FlashAlgo development.
 -  An evaluation board with a target MCU, debug probe or an integrated interface chip. The hardware [is reviewed in greater details later in this document]().
 
     The new target needs a unique board ID. [Contact Arm]()<!-- need a link here --> to get one.