Add keywords field to platform manifest

Author: valeros

platform.json

@@ -4,6 +4,13 @@
   "description": "Espressif Systems is a privately held fabless semiconductor company. They provide wireless communications and Wi-Fi chips which are widely used in mobile devices and the Internet of Things applications.",
   "homepage": "https://espressif.com/",
   "license": "Apache-2.0",
+  "keywords": [
+      "dev-platform",
+      "Wi-Fi",
+      "Bluetooth",
+      "Xtensa",
+      "LX6"
+  ],
   "engines": {
     "platformio": "<5"
   },