Add provisioning script for ARM64 GitHub runners

Signed-off-by: Stefan Prodan <stefan.prodan@gmail.com>

.github/runners/README.md

@@ -0,0 +1,42 @@
+# Flux GitHub runners
+
+How to provision GitHub Actions self-hosted runners for Flux conformance testing.
+
+## ARM64 Instance specs
+
+In order to add a new runner to the GitHub Actions pool,
+first create an instance on Oracle Cloud with the following configuration:
+- OS: Canonical Ubuntu 20.04
+- Shape: VM.Standard.A1.Flex
+- OCPU Count: 2 
+- Memory (GB): 12
+- Network Bandwidth (Gbps): 2
+- Local Disk: Block Storage Only  
+
+Note that the instance image source must be **Canonical Ubuntu** instead of the default Oracle Linux.
+
+## ARM64 Instance setup
+
+- SSH into a newly created instance
+```shell
+ssh ubuntu@<instance-public-IP>
+``` 
+- Create the action runner dir
+```shell
+mkdir -p actions-runner && cd actions-runner
+```
+- Download the provisioning script
+```shell
+curl -sL https://raw.githubusercontent.com/fluxcd/flux2/main/.github/runners/arm64.sh > arm64.sh \
+  && chmod +x ./arm64.sh
+```
+- Retrieve the GitHub runner token from the repository [settings page](https://github.com/fluxcd/flux2/settings/actions/runners/new?arch=arm64&os=linux)
+- Run the provisioning script passing the token as the first argument
+```shell
+sudo ./arm64.sh <TOKEN>
+```
+- Reboot the instance
+```shell
+sudo reboot
+```  
+- Navigate to the GitHub repository [runners page](https://github.com/fluxcd/flux2/settings/actions/runners) and check the runner status