Nimble: Update documentation to include distinction between upstream

mesh example and ESP-BLE-MESH

components/bt/host/nimble/Kconfig.in

@@ -314,7 +314,10 @@ menuconfig BT_NIMBLE_MESH
     depends on BT_NIMBLE_ENABLED
     default n
     help
-        Enable BLE Mesh functionality
+        Enable BLE Mesh example present in upstream mynewt-nimble and not maintained by Espressif.
+
+        IDF maintains ESP-BLE-MESH as the official Mesh solution. Please refer to ESP-BLE-MESH guide at:
+        `https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-guides/esp-ble-mesh/ble-mesh-index.html`
 
 config BT_NIMBLE_MESH_PROXY
     bool "Enable mesh proxy functionality"

examples/bluetooth/nimble/blemesh/README.md

@@ -3,6 +3,11 @@
 
 # BLE Mesh example
 
+This example is part of upstream mynewt-nimble implementation and not maintained by Espressif.
+
+IDF maintains ESP-BLE-MESH as the official Mesh solution. Please refer to ESP-BLE-MESH guide at:
+https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-guides/esp-ble-mesh/ble-mesh-index.html
+
 (See the README.md file in the upper level 'examples' directory for more information about examples.)
 
 This example implements Bluetooth Mesh node that supports On/Off and Level models.