Add DOCKER_README and update README with Docker section (#703)

Author: VladislavFitz

DOCKER_README.MD

@@ -0,0 +1,79 @@
+In this page you will find our recommended way of installing Docker on your machine.
+This guide is made for OSX users.
+
+## Install docker
+
+First install Docker using [Homebrew](https://brew.sh/)
+```
+$ brew install docker
+```
+
+You can then install [Docker Desktop](https://docs.docker.com/get-docker/) if you wish, or use `docker-machine`. As we prefer the second option, we will only document this one.
+
+## Setup your docker
+
+Install `docker-machine`
+```
+$ brew install docker-machine
+```
+
+Then install [VirtualBox](https://www.virtualbox.org/) with [Homebrew Cask](https://github.com/Homebrew/homebrew-cask) to get a driver for your Docker machine
+```
+$ brew cask install virtualbox
+```
+
+You may need to enter your password and authorize the application in your `System Settings` > `Security & Privacy`.
+
+Create now a new machine, set it up as default and connect your shell to it (here we use zsh. The commands should anyway be displayed in each steps' output)
+
+```
+$ docker-machine create --driver virtualbox default
+$ docker-machine env default
+$ eval "$(docker-machine env default)"
+```
+
+Now you're all setup to use our provided Docker image!
+
+## Build the image
+
+```bash
+docker build -t algolia-swift .
+```
+
+## Run the image
+
+You need to provide few environment variables at runtime to be able to run the [Common Test Suite](https://github.com/algolia/algoliasearch-client-specs/tree/master/common-test-suite).
+You can set them up directly in the command:
+
+```bash
+docker run -it --rm --env ALGOLIA_APP_ID=XXXXXX [...] -v $PWD:/app -w /app algolia-swift bash
+```
+
+However, we advise you to export them in your `.bashrc` or `.zshrc`. That way, you can use [Docker's shorten syntax](https://docs.docker.com/engine/reference/commandline/run/#set-environment-variables--e---env---env-file) to set your variables.
+
+```bash
+### For external contributors, only the following env variables should be enough
+docker run -it --rm --env ALGOLIA_APPLICATION_ID_1 \
+                    --env ALGOLIA_ADMIN_KEY_1 \
+                    --env ALGOLIA_SEARCH_KEY_1 \
+-v $PWD:/app -w /app algolia-swift bash
+
+### This is needed only to run the full test suite
+docker run -it --rm --env ALGOLIA_APPLICATION_ID_1 \
+                    --env ALGOLIA_ADMIN_KEY_1 \
+                    --env ALGOLIA_SEARCH_KEY_1 \
+                    --env ALGOLIA_APPLICATION_ID_2 \
+                    --env ALGOLIA_ADMIN_KEY_2 \
+                    --env ALGOLIA_APPLICATION_ID_MCM \
+                    --env ALGOLIA_ADMIN_KEY_MCM \
+-v $PWD:/app -w /app algolia-swift bash
+```
+
+Once your container is running, any changes you make in your IDE are directly reflected in the container.
+
+To launch the tests, you can use the following command
+```shell script
+swift test
+```
+
+Feel free to contact us if you have any questions.

README.md

@@ -196,6 +196,10 @@ For full documentation, visit the [Algolia Swift API Client's documentation](htt
 
 You can find code samples in the [Algolia's API Clients playground](https://github.com/algolia/api-clients-playground/tree/master/swift).
 
+## Use the Dockerfile
+
+If you want to contribute to this project without installing all its dependencies, you can use our Docker image. Please check our [dedicated guide](DOCKER_README.MD) to learn more.
+
 ## 📄 License
 
 Algolia Swift API Client is an open-sourced software licensed under the [MIT license](LICENSE).