Document how to add Windows self-hosted runners (#1608)

* adding windows docs

* adding windows docs

* Editing the explanations

* Update README.md

* Update README.md

Co-authored-by: Yusuke Kuoka <ykuoka@gmail.com>

README.md

@@ -41,6 +41,7 @@ ToC:
   - [Using IRSA (IAM Roles for Service Accounts) in EKS](#using-irsa-iam-roles-for-service-accounts-in-eks)
   - [Software Installed in the Runner Image](#software-installed-in-the-runner-image)
   - [Using without cert-manager](#using-without-cert-manager)
+  - [Windows Runners](#setting-up-windows-runners)
   - [Multitenancy](#multitenancy)
 - [Troubleshooting](#troubleshooting)
 - [Contributing](#contributing)
@@ -1764,6 +1765,118 @@ $ helm --upgrade install actions-runner-controller/actions-runner-controller \
   admissionWebHooks.caBundle=${CA_BUNDLE}
 ```
 
+### Setting up Windows Runners
+
+The main two steps in enabling Windows self-hosted runners are:
+
+- Using `nodeSelector`'s property to filter the `cert-manger` and `actions-runner-controller` pods
+- Deploying a RunnerDeployment using a Windows-based image
+
+For the first step, you need to set the `nodeSelector.kubernetes.io/os` property in both the `cert-manager` and the `actions-runner-controller` deployments to `linux` so that the pods for these two deployments are only scheduled in Linux nodes. You can do this as follows:
+
+```yaml
+nodeSelector:
+  kubernetes.io/os: linux
+```
+
+`cert-manager` has 4 different application within it the main application, the `webhook`, the `cainjector` and the `startupapicheck`. In the parameters or values file you use for the deployment you need to add the `nodeSelector` property four times, one for each application.
+
+For the `actions-runner-controller` you only have to use the `nodeSelector` only for the main deployment, so it only has to be set once.
+
+Once this is set up, you will need to deploy two different `RunnerDeployment`'s, one for Windows and one for Linux.
+The Linux deployment can use either the default image or a custom one, however, there isn't a default Windows image so for Windows deployments you will have to build your own image.
+
+Below we share an example of the YAML used to create the deployment for each Operating System and a Dockerfile for the Windows deployment. 
+
+<details><summary>Windows</summary>
+<p>
+
+#### RunnerDeployment
+
+```yaml
+---
+apiVersion: actions.summerwind.dev/v1alpha1
+kind: RunnerDeployment
+metadata:
+  name: k8s-runners-windows
+  namespace: actions-runner-system
+spec:
+  template:
+    spec:
+      image: <repo>/<image>:<windows-tag>
+      dockerdWithinRunnerContainer: true
+      nodeSelector:
+        kubernetes.io/os: windows
+        kubernetes.io/arch: amd64
+      repository: <owner>/<repo>
+      labels:
+        - windows
+        - X64
+        - devops-managed
+```
+
+#### Dockerfile
+
+> Note that you'd need to patch the below Dockerfile if you need a graceful termination.
+> See https://github.com/actions-runner-controller/actions-runner-controller/pull/1608/files#r917319574 for more information.
+
+```Dockerfile
+FROM mcr.microsoft.com/windows/servercore:ltsc2019
+
+WORKDIR /actions-runner
+
+SHELL ["powershell", "-Command", "$ErrorActionPreference = 'Stop';$ProgressPreference='silentlyContinue';"]
+
+RUN Invoke-WebRequest -Uri https://github.com/actions/runner/releases/download/v2.292.0/actions-runner-win-x64-2.292.0.zip -OutFile actions-runner-win-x64-2.292.0.zip
+
+RUN if((Get-FileHash -Path actions-runner-win-x64-2.292.0.zip -Algorithm SHA256).Hash.ToUpper() -ne 'f27dae1413263e43f7416d719e0baf338c8d80a366fed849ecf5fffcec1e941f'.ToUpper()){ throw 'Computed checksum did not match' }
+
+RUN Add-Type -AssemblyName System.IO.Compression.FileSystem ; [System.IO.Compression.ZipFile]::ExtractToDirectory('actions-runner-win-x64-2.292.0.zip', $PWD)
+
+RUN Invoke-WebRequest -Uri 'https://aka.ms/install-powershell.ps1' -OutFile install-powershell.ps1; ./install-powershell.ps1 -AddToPath
+
+RUN powershell Set-ExecutionPolicy Bypass -Scope Process -Force; [System.Net.ServicePointManager]::SecurityProtocol = [System.Net.ServicePointManager]::SecurityProtocol -bor 3072; iex ((New-Object System.Net.WebClient).DownloadString('https://community.chocolatey.org/install.ps1'))
+
+RUN powershell choco install git.install --params "'/GitAndUnixToolsOnPath'" -y
+
+RUN powershell choco feature enable -n allowGlobalConfirmation
+
+CMD [ "pwsh", "-c", "./config.cmd --name $env:RUNNER_NAME --url https://github.com/$env:RUNNER_REPO --token $env:RUNNER_TOKEN --labels $env:RUNNER_LABELS --unattended --replace --ephemeral; ./run.cmd"]
+```
+</p>
+</details>
+
+
+<details><summary>Linux</summary>
+<p>
+
+#### RunnerDeployment
+
+```yaml
+---
+apiVersion: actions.summerwind.dev/v1alpha1
+kind: RunnerDeployment
+metadata:
+  name: k8s-runners-linux
+  namespace: actions-runner-system
+spec:
+  template:
+    spec:
+      image: <repo>/<image>:<linux-tag>
+      nodeSelector:
+        kubernetes.io/os: linux
+        kubernetes.io/arch: amd64
+      repository: <owner>:<repo>
+      labels:
+        - linux
+        - X64
+        - devops-managed
+```
+</p>
+</details>
+
+After both `RunnerDeployment`'s are up and running, you can now proceed to deploy the `HorizontalRunnerAutoscaler` for each deployment.
+
 ### Multitenancy
 
 > This feature requires controller version => [v0.26.0](https://github.com/actions-runner-controller/actions-runner-controller/releases/tag/v0.26.0)