Add MKRGSM and MKRNB links

Author: sandeepmistry

README.md

@@ -10,6 +10,8 @@ Derived from [Adrian McEwen's HttpClient library](https://github.com/amcewen/Htt
   - [WiFiNINA](https://github.com/arduino-libraries/WiFiNINA)
   - [WiFi101](https://github.com/arduino-libraries/WiFi101)
   - [Ethernet](https://github.com/arduino-libraries/Ethernet)
+  - [MKRGSM](https://github.com/arduino-libraries/MKRGSM)
+  - [MKRNB](https://github.com/arduino-libraries/MKRNB)
   - [WiFi](https://github.com/arduino-libraries/WiFi)
   - [GSM](https://github.com/arduino-libraries/GSM)