Adding a README.md for the hack folder.

Signed-off-by: Abhishek Sharma <abhishek@asharma.me>

hack/README.md

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+## About
+
+This directory contains a collection of scripts used to build and manage this
+repository. If there are any issues regarding the intention of a particular
+script (or even part of a certain script), please reach out to us.
+It may help us either refine our current scripts, or add on new ones
+that are appropriate for a given use case.
+
+## DinD (dind.sh)
+
+DinD is a wrapper script which allows Docker to be run inside a Docker
+container. DinD requires the container to
+be run with privileged mode enabled.
+
+## Generate Authors (generate-authors.sh)
+
+Generates AUTHORS; a file with all the names and corresponding emails of
+individual contributors. AUTHORS can be found in the home directory of
+this repository.
+
+## Install (install.sh)
+
+Executable install script for installing Docker. If updates to this are
+desired, please use hack/release.sh during a normal release. The following
+one-liner may be used for script hotfixes:
+
+- `aws s3 cp --acl public-read hack/install.sh s3://get.docker.com/index`
+
+## Make
+
+There are two make files, each with different extensions. Neither are supposed
+to be called directly; only invoke `make`. Both scripts run inside a Docker
+container.
+
+### make.ps1
+
+- The Windows native build script that uses PowerShell semantics; it is limited
+unlike `hack\make.sh` since it does not provide support for the full set of
+operations provided by the Linux counterpart, `make.sh`. However, `make.ps1`
+does provide support for local Windows development and Windows to Windows CI.
+More information is found within `make.ps1` by the author, @jhowardmsft
+
+### make.sh
+
+- Referenced via `make test` when running tests on a local machine,
+or directly referenced when running tests inside a Docker development container.  
+- When running on a local machine, `make test` to run all tests found in
+`test`, `test-unit`, `test-integration-cli`, and `test-docker-py` on
+your local machine. The default timeout is set in `make.sh` to 60 minutes
+(`${TIMEOUT:=60m}`), since it currently takes up to an hour to run
+all of the tests.
+- When running inside a Docker development container, `hack/make.sh` does
+not have a single target that runs all the tests. You need to provide a
+single command line with multiple targets that performs the same thing.
+An example referenced from [Run targets inside a development container](https://docs.docker.com/opensource/project/test-and-docs/#run-targets-inside-a-development-container): `root@5f8630b873fe:/go/src/github.com/moby/moby# hack/make.sh dynbinary binary cross test-unit test-integration-cli test-docker-py`
+- For more information related to testing outside the scope of this README,
+refer to
+[Run tests and test documentation](https://docs.docker.com/opensource/project/test-and-docs/)
+
+## Release (release.sh)
+
+Releases any bundles built by `make` on a public AWS S3 bucket.
+For information regarding configuration, please view `release.sh`.
+
+## Vendor (vendor.sh)
+
+A shell script that is a wrapper around Vndr. For information on how to use
+this, please refer to [vndr's README](https://github.com/LK4D4/vndr/blob/master/README.md)