[docs] Run e2e tests in platform=none

This commit adds section in HACKING.md to describe the process
of running the e2e tests on a platform-agnostic infrastructure.

docs/HACKING.md

@@ -117,6 +117,40 @@ hack/run-ci-e2e-test.sh -s -m 2 -c 1
 ```
 Please note that you do not need to run `hack/olm.sh run` before `hack/run-ci-e2e-test.sh`.
 
+### Running e2e tests on platform-agnostic infrastructure
+
+To run the WMCO' e2e tests on a bare metal or other platform-agnostic infrastructure (platform=none), where there
+is no cloud provider specification, the desired number of Windows instances must be available beforehand, and you
+need provide the instance(s) information to the e2e test suite using an environment variable.
+
+To deploy machines in any of the [infrastructure providers supported by WMCO](wmco-prerequisites.md#supported-cloud-providers-based-on-okdocp-version-and-wmco-version),
+refer to the specific provider documentation. See Windows instance [pre-requisites](https://github.com/openshift/windows-machine-config-operator/blob/master/docs/byoh-instance-pre-requisites.md).
+
+The information you need to collect from each Windows instance is:
+- the internal IP address, and
+- the Windows administrator username
+
+Export `WINDOWS_INSTANCES_DATA` as an environment variable with the corresponding [windows-instances configMap](https://github.com/openshift/windows-machine-config-operator#adding-instances)
+data section, and a new `windows-instances` configMap will be created during the execution of the e2e test suite.
+
+For example:
+```shell
+export WINDOWS_INSTANCES_DATA='
+data:
+  10.1.42.1: |-
+    username=Administrator
+'
+```
+where `10.1.42.1` is the IP address and `Administrator` is the Windows' administrator username of the Windows instance.
+
+Once the `WINDOWS_INSTANCES_DATA` environment variable is declared and exported you can run:
+```shell
+hack/run-ci-e2e-test.sh -m 0 -c 1
+```
+where, `-m 0` indicates no Windows instance will be configured by the Windows Machine controller and `-c 1`
+accounts for the number of instances that will be configured by the ConfigMap controller, and must match the
+number of entries in the `WINDOWS_INSTANCES_DATA` environment variable, in this example only one (1).
+
 ## Bundling the Windows Machine Config Operator
 This directory contains resources related to installing the WMCO onto a cluster using OLM.