Install & Upgrade guidance for Release notes

[asoorm]

In the release notes for our operator - we currently have a section called Docker images which I am not certain if it is that useful.

I think that we can deprecate this section, and replace it with 2 headings moving forward:

• Install
• Upgrade

Largely, these sections should be the same for every release, however the Upgrade notes will also identify breaking changes.

[gernest]

makes sense. Since from v0.8.0 we will be using the helm repository for installation, the section willl be any chages that are helm chart specific.