Added doc about docker images

tools/docker/README.md

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+# Espressif's SDK for Matter Docker Image
+
+This is a Docker image for the [Espressif's SDK for Matter (ESP-MATTER)](https://github.com/espressif/esp-matter). It is intended for building applications of ESP-IDF that uses Espressif's SDK for Matter, when doing automated builds.
+
+This image contains a copy of the Espressif's SDK for Matter and uses the v4.4.2 release ESP-IDF Docker image to build ESP-IDF projects that use Espressif's SDK for Matter.
+
+## Tags
+
+Multiple tags of this image are maintained:
+
+- `latest`: tracks `master` branch of ESP-MATTER
+- `chip`: 
+
+## Basic Usage
+
+Build a project located in the current directory using `idf.py build` command:
+
+```bash
+docker run --rm -v $PWD:/project -w /project espressif/esp-matter:latest idf.py build
+```
+## Building custom images
+
+The Dockerfile in Espressif's SDK for Matter repository provides several build arguments which can be used to customize the Docker image:
+
+These are the different build arguments that can be used:
+- `ESP_IDF_TAG`: Espressif idf Docker image tag, default is v4.4.2. Check all the available tags at [Docker Hub](https://hub.docker.com/r/espressif/idf/tags).
+- `ESP_MATTER_CLONE_URL`: URL of the repository to clone ESP-IDF Espressif's SDK for Matter. Can be set to a custom URL when working with a fork of ESP-IDF. Default is `https://github.com/espressif/esp-matter.git`.
+- `ESP_MATTER_CLONE_BRANCH_OR_TAG`: Name of a git branch or tag use when cloning ESP-IDF. This value is passed to `git clone` command using the `--branch` argument. Default is `main`.
+- `ESP_MATTER_CHECKOUT_REF`: If this argument is set to a non-empty value, `git checkout $ESP_MATTER_CHECKOUT_REF` command will be performed after cloning. This argument can be set to the SHA of the specific commit to check out, for example if some specific commit on a release branch is desired.
+- `ESP_MATTER_CLONE_SHALLOW`: If this argument is set to a non-empty value, It will perform a shallow clone that only downloads the required submodules by Matter for ESP32 platform using [`checkout_submodules.py`](https://github.com/project-chip/connectedhomeip/blob/master/scripts/checkout_submodules.py). If it is empty will clone recursively all the submodules from Matter repository.