Extension: add Siyeenove mShield (#6640)

Author: martinwork

docs/extensions/extension-gallery.md

@@ -561,6 +561,10 @@ Many extensions are available to work with interface kits, add-on hardware, or o
 
 ```codecard
 [{
+  "name": "Siyeenove mShield",
+  "url":"/pkg/siyeenove/pxt_mshield",
+  "cardType": "package"
+}, {
   "name": "BrailleBot",
   "url":"/pkg/roborisen/braillebot",
   "cardType": "package"

targetconfig.json

@@ -432,6 +432,7 @@
             "smarthon/pxt-smarthome": { "tags": [ "Networking" ] },
             "roborisen/braillebot": { "tags": [ "Robotics" ] },
             "backyardbrains/pxt-spikerbit": { "tags": [ "Science" ] },
+            "siyeenove/pxt_mshield": { "tags": [ "Robotics" ] },
             "microsoft/pxt-simx-sample": {
                 "simx": {
                     "sha": "7301f5900879b85127482d79bab48f03c25690a8",