Fix up PM sentence in the 4.0 RN and add more information in the section "Disabling applications"

[moffatsadeghi]

Fix up this sentence in the 4.0 release notes and add more information in the section "Disabling applications" for better clarity:

• Fix up: "To enable the Project Manager, simply follow the instructions in Disabling applications to enable this application."

Link to 4.0 release section I am speaking of: https://osc.github.io/ood-documentation/latest/release-notes/v4.0-release-notes.html#project-manager-preview

A suggestion could be "To enable the Project Manager, refer to the instructions in the Disabling applications section, which also explain how to enable this application."

• Add some more clarity in the Disabling applications section in our documentation to talk about enabling applications. Truthfully, if folks have sys admin / sudo permissions, they know what they are doing. But our documentation could be a bit clearer here on toggling applications and how to do this.