Add docker file to fix Zephy ESP32 linking issue (#2314)

- Provide a Dockerfile.old to fix issue of ESP32 custom linker scripts not working
  properly with the newer version of Zephyr, as reported in #2263
- Provide a Dockerfile with newer Zephyr for other boards
- Update the corresponding document

product-mini/platforms/zephyr/simple/README.md

@@ -0,0 +1,106 @@
+# How to use WAMR with Zephyr
+
+## Build with Docker(recommend approach)
+
+To have a quicker start, a Docker container of the Zephyr setup can be generated. The current docker image would be considerably large(~15GB), it would take some time to build it and enough disk space to store it.
+
+### Build Docker images
+
+```shell
+docker build -t wamr-zephyr .
+```
+
+> PS: currently, the esp32 custom linker script only works with a lower version of Zephyr, if you want to use an esp32 board, you can build the Dockerfile with a lower version of Zephyr, Zephyr SDE, ESP-IDF. The old version of Docker image can also build other targets, but probably it's a better choice to use the new Dockerfile for other boards
+
+```shell
+# If you want to build on esp32 platform
+docker build -f Dockerfile.old -t wamr-zephyr .
+```
+
+### Run Docker images
+
+Adopt the device or remove if not needed.
+
+```shell
+docker run -ti --device=/dev/ttyUSB0 wamr-zephyr
+```
+
+And then inside the docker container:
+
+```shell
+# copy the corresponding board conf file to current directory
+cp boards/qemu_x86_nommu.conf prj.conf
+# then build
+./build_and_run.sh x86
+```
+
+> PS: for boards esp32, need to configure some environment first
+
+```shell
+# configure zephyr with espressif
+export ZEPHYR_TOOLCHAIN_VARIANT="espressif"
+export ESPRESSIF_TOOLCHAIN_PATH="/root/.espressif/tools/xtensa-esp32-elf/esp-2019r2-8.2.0/xtensa-esp32-elf/"
+export ESP_IDF_PATH="/root/esp/esp-idf"
+# copy the corresponding board conf file to current directory
+cp boards/esp32.conf prj.conf
+# then build
+./build_and_run.sh esp32
+```
+
+## Build on local environment
+
+### Dependencies installation
+
+Following the Zephyr and Espressif official document:
+
+1. Zephyr installation:
+
+   <https://docs.zephyrproject.org/latest/develop/getting_started/index.html>
+
+2. ESP32 installation:
+
+   <https://docs.espressif.com/projects/esp-idf/en/latest/esp32/get-started/linux-macos-setup.html>
+
+And setup the Zephyr for esp32:
+
+<https://wiki.amarulasolutions.com/zephyr/esp32/esp32-setup.html>
+
+Then Installing QEMU, for example, on Linux:
+
+```shell
+sudo apt-get install qemu
+```
+
+### Run the build script
+
+Make sure you have the environment variable ready, you can use the command `env` to check:
+
+```shell
+env
+```
+
+```shell
+# export ZEPHYR_BASE if it's not present
+export ZEPHYR_BASE=~/zephyrproject/zephyr
+# and if you install zephyr in virtual environment rather than global
+source ~/zephyrproject/.venv/bin/activate
+```
+
+For boards esp32, need to configure some extra environment first, check the following env variable whether in the env list, if not, add them like:
+
+> Noted: The esp32 custom linker script doesn't work with the recent version of Zephyr, if you want to use it in the local environment, please install Zephyr 2.3.0 with the corresponding SDK, and ESP-IDF 4.0
+
+```shell
+export ZEPHYR_TOOLCHAIN_VARIANT="espressif"
+export ESPRESSIF_TOOLCHAIN_PATH="~/.espressif/tools/xtensa-esp32-elf/esp-{the version you installed}/xtensa-esp32-elf/"
+export ESP_IDF_PATH="~/esp/esp-idf"
+```
+
+Then you can run the build script:
+
+```shell
+# copy the corresponding board conf file to current directory
+cp boards/qemu_x86_nommu.conf prj.conf
+# then build
+./build_and_run.sh x86
+```