add nimble mesh example

need meshctl installed on raspberrypi. nimble offical samples have a lot of pit ...

examples/nimble_mesh_models_example_1/README.md

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+### Bluetooth: Mesh OnOff Model
+
+
+#### Overview
+
+This is a simple application demonstrating a Bluetooth mesh multi-element node.
+Each element has a mesh onoff client and server
+model which controls one of the 4 sets of buttons and LEDs .
+
+Prior to provisioning, an unprovisioned beacon is broadcast that contains
+a UUID. Each button controls the state of its
+corresponding LED and does not initiate any mesh activity.
+
+The models for button 1 and LED 1 are in the node's root element.
+The 3 remaining button/LED pairs are in elements 1 through 3.
+Assuming the provisioner assigns 0x100 to the root element,
+the secondary elements will appear at 0x101, 0x102 and 0x103.
+
+After provisioning, the button clients must
+be configured to publish and the LED servers to subscribe.
+
+If a LED server is provided with a publish address, it will
+also publish its status on an onoff state change.
+
+If a button is pressed only once within a 1 second interval, it sends an
+"on" message. If it is pressed more than once, it
+sends an "off" message. The buttons are quite noisy and are debounced in
+the button_pressed() interrupt handler. An interrupt within 250ms of the
+previous is discarded. This might seem a little clumsy, but the alternative of
+using one button for "on" and another for "off" would reduce the number
+of onoff clients from 4 to 2.
+
+#### Requirements
+************
+
+This sample has been tested on the Nordic nRF52840-PDK board, but would
+likely also run on the nrf52_pca10040 board.
+
+#### Building and Running
+********************
+
+Prior to provisioning, each button controls its corresponding LED as one
+would expect with an actual switch.
+
+Provisioning is done using the BlueZ meshctl utility. Below is an example that
+binds button 2 and LED 1 to application key 1. It then configures button 2
+to publish to group 0xc000 and LED 1 to subscribe to that group.
+
+```
+discover-unprovisioned on
+provision <discovered UUID>
+menu config
+target 0100
+appkey-add 1
+bind 0 1 1000                # bind appkey 1 to LED server on element 0 (unicast 0100)
+sub-add 0100 c000 1000       # add subscription to group address c000 to the LED server
+bind 1 1 1001                # bind appkey 1 to button 2 on element 1 (unicast 0101)
+pub-set 0101 c000 1 0 0 1001 # publish button 2 to group address c000
+```
+
+The meshctl utility maintains a persistent JSON database containing
+the mesh configuration. As additional nodes (boards) are provisioned, it
+assigns sequential unicast addresses based on the number of elements
+supported by the node. This example supports 4 elements per node.
+
+The first or root element of the node contains models for configuration,
+health, and onoff. The secondary elements only
+have models for onoff. The meshctl target for configuration must be the
+root element's unicast address as it is the only one that has a
+configuration server model.
+
+If meshctl is gracefully exited, it can be restarted and reconnected to
+network 0x0.
+
+The meshctl utility also supports a onoff model client that can be used to
+change the state of any LED that is bound to application key 0x1.
+This is done by setting the target to the unicast address of the element
+that has that LED's model and issuing the onoff command.
+Group addresses are not supported.