Update documentation for Helm installation

[jz543fm]

What would you like to be added:

Better documentation for installation process for PipeCD, I can not understand how can I deploy pipecd with (Minio and MySQL) configuration via Helm, it's not very well documented for Minio and MySQL and how to use --set-file ((access_key & secret_key)) with minio and MySQL, it would be more helpful with example how it should looks like

Why is this needed:

Very hard to understand the installation process and I do not understand from documentation how should I use --set-file for Minio and SQL for example ( access_key and secret_key), on the installation page is only example for Firestore & GCP

[jz543fm]

Fixed