Update testing documentation with tool installation directions

Fixing a couple of variable declarations that were being
complained about by ``make lint``.

Edit: Updated the Testing.MD doc to add references to the
hack scripts.

Addresses: #575

Author: demonCoder95

docs/testing.md

@@ -36,3 +36,66 @@ Run linters test before pushing your commit
 ```bash
 make lint
 ```
+
+## Using the Hack scripts
+
+The repository contains a ``hack`` directory which has some very useful scripts
+for setting up containerized testing environments. It also has Dockerfiles to
+allow you to generate images for your own use.
+
+All the scripts accept the ``CONTAINER_RUNTIME`` environment variable with default
+of ``podman``. This you can edit to ``docker`` as well.
+
+### Example of running ``golint`` in a Docker container
+
+1. Start by setting the environment variable appropriately
+
+    ```bash
+    export CONTAINER_RUNTIME=docker
+    ```
+
+2. From the operator parent dir, you can invoke the hack scripts
+
+    ```bash
+    ./hack/golint.sh
+    ```
+
+    **Note** It's important to be in the operator parent dir because it
+    contains the ``Makefile`` that is used in running the tests for the
+    operator. Otherwise, you'll see the following error
+
+    ```bash
+    sh: 0: Can't open /go/src/github.com/metal3-io/baremetal-operator/hack/golint.sh
+    ```
+
+3. Upon successful execution, you should see the following output. I already
+    had all the images available from a previous run, you might see the images
+    getting downloaded if you're running for the very first time.
+
+    ```bash
+    + IS_CONTAINER=false
+    + CONTAINER_RUNTIME=docker
+    + [ false != false ]
+    + docker run --rm --env IS_CONTAINER=TRUE --volume /home/noor/go/src/github.com/metal3-io/baremetal-operator:/go/src/github.com/metal3-io/baremetal-operator:ro,z\
+    --entrypoint sh --workdir /go/src/github.com/metal3-io/baremetal-operator\
+    quay.io/metal3-io/golint:latest /go/src/github.com/metal3-io/baremetal-operator/hack/golint.sh
+    + IS_CONTAINER=TRUE
+    + CONTAINER_RUNTIME=podman
+    + [ TRUE != false ]
+    + export XDG_CACHE_HOME=/tmp/.cache
+    + make lint
+    which golint 2>&1 >/dev/null || make OPATH/bin/golint
+    find ./pkg ./cmd -type f -name \*.go  |grep -v zz_ | xargs -L1 golint -set_exit_status
+    ```
+
+## Getting the latest tooling
+
+For testing without the hack scripts, make sure you install the latest
+development tools using ``go get``, e-g
+
+```bash
+go get golang.org/x/lint/golint
+```
+
+This ensures that the linters you have locally and the ones running in the CI
+are matched and helps avoid inconsistencies. Happy coding!