feat(wifi_remote): Add support for simple eppp based RPC

components/esp_wifi_remote/examples/mqtt/README.md

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+# MQTT demo application that runs on linux
+
+## Overview
+
+This is a simple example demonstrating connecting to an MQTT broker, subscribing and publishing some data.
+This example uses IDF build system and could be configured to be build and executed:
+* for any ESP32 family chip
+* for linux target
+
+## How to use example
+
+### Hardware Required
+
+To run this example, you need any ESP32 development board or just PC/virtual machine/container running linux operating system.
+
+### Host build modes
+
+Linux build is supported in these two modes:
+* `WITH_LWIP=0`: Without lwIP component. The project uses linux BSD socket interface to interact with TCP/IP stack. There's no connection phase, we use the host network as users. This mode is often referred to as user-side networking.
+* `WITH_LWIP=1`: Including lwIP component, which is added to the list of required components and compiled on host. In this mode, we have to map the host network (linux TCP/IP stack) to the target network (lwip). We use IDF's [`tapif_io`](https://github.com/espressif/esp-idf/tree/master/examples/common_components/protocol_examples_tapif_io) component to create a network interface, which will be used to pass packets to and from the simulated target. Please refer to the [README](https://github.com/espressif/esp-idf/tree/master/examples/common_components/protocol_examples_tapif_io#readme) for more details about the host side networking.
+
+### Building on linux
+
+1) Configure linux target
+```bash
+idf.py --preview set-target linux
+```
+
+2) Build the project with preferred components (with or without lwip)
+```bash
+idf.py -DWITH_LWIP=0 build  # Building without lwip (user networking)
+idf.py -DWITH_LWIP=1 build  # Building with lwip (TAP networking)
+```
+
+3) Run the project
+
+It is possible to run the project elf file directly, or using `idf.py` monitor target (no need to flash):
+```bash
+idf.py monitor
+```
+idf.py -DWITH_LWIP=0 build  # Building without lwip (user networking)