Describe upcoming CI minutes tracking changes

Why is this change being made?

We plan to start tracking Shared Runners CI minutes for public projects.
We need to update our pricing Q&A accordingly.
More details may be found in gitlab-org/gitlab#210570 (closed)

⚠ The text needs to be carefully reviewed by stakeholders. It was not approved, I created this MR as a reminder that we will need to make this change.

How will this merge request impact page speed?

No changes are expected

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what