docs: included instructions to docker login to access ghcr (#1891)

# Description

Added a note in the installation documentation to include instructions
for authenticating to GitHub Container Registry, before installing
Retina via Helm.
This ensures users avoid credential errors when pulling images.
(my first pr)

## Related Issue

This pull request is related to #631 

## Checklist

- [x] I have read the [contributing
documentation](https://retina.sh/docs/Contributing/overview).
- [x] I signed and signed-off the commits (`git commit -S -s ...`). See
[this
documentation](https://docs.github.com/en/authentication/managing-commit-signature-verification/about-commit-signature-verification)
on signing commits.
- [x] I have correctly attributed the author(s) of the code.
- [x] I have tested the changes locally.
- [x] I have followed the project's style guidelines.
- [x] I have updated the documentation, if necessary.
- [x] I have added tests, if applicable.

## Screenshots (if applicable) or Testing Completed

Please add any relevant screenshots or GIFs to showcase the changes
made.

## Additional Notes

Add any additional notes or context about the pull request here.

---

Please refer to the [CONTRIBUTING.md](../CONTRIBUTING.md) file for more
information on how to contribute to this project.

Signed-off-by: letv1nnn <[email protected]>
Signed-off-by: letv1nnn <[email protected]>

Author: letv1nnn

docs/02-Installation/01-Setup.md

@@ -64,6 +64,10 @@ helm upgrade --install retina oci://ghcr.io/microsoft/retina/charts/retina \
 
 ### Standard Control Plane
 
+>NOTE: Before installing Retina via Helm, you need to authenticate to [GitHub Container Registry (GHCR)](https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-container-registry) to pull the required images.
+
+Run the following command: `docker login ghcr.io`
+
 #### Basic Mode
 
 ```shell