Add PI workflow to Product PI Page

Why is this change being made?

This MR adds the PI workflow to the Product Team PI Page. The PI workflow was presented in the Weekly Product Meeting on August 11, 2020, for a recap of the presentation, please see the slide deck and watch the video presentation.

The PI workflow outlines the steps required for putting a product performance indicator in place. The objective of the PI workflow is to help the product organization achieve the Product Organizations FY21-Q3 OKRs:

• 100% of groups have Future GMAU (or Paid GMAU) with instrumentation, dashboards, and quarterly targets
• 100% of stages have Future SMAU and Paid SMAU with instrumentation, dashboards, and quarterly targets.

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per [say-why-not-just-what][transparency]
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to your manager.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in [#mr-buddies][mr-buddies-slack].
  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files.