add an example about how to use Kconfig file

Signed-off-by: Nicola Lunghi <nicola.lunghi@jci.com>

main/Kconfig.projbuild

@@ -0,0 +1,14 @@
+# put here your custom config value
+menu "Example Configuration"
+config ESP_WIFI_SSID
+    string "WiFi SSID"
+    default "myssid"
+    help
+	SSID (network name) for the example to connect to.
+
+config ESP_WIFI_PASSWORD
+    string "WiFi Password"
+    default "mypassword"
+    help
+	WiFi password (WPA or WPA2) for the example to use.
+endmenu

main/main.c

@@ -22,8 +22,8 @@ void app_main(void)
     ESP_ERROR_CHECK( esp_wifi_set_mode(WIFI_MODE_STA) );
     wifi_config_t sta_config = {
         .sta = {
-            .ssid = "access_point_name",
+            .ssid = CONFIG_ESP_WIFI_SSID,
-            .password = "password",
+            .password = CONFIG_ESP_WIFI_PASSWORD,
             .bssid_set = false
         }
     };