Update the API Guide with Code mapping template & instructions

[jillian-hammer]

Problem statement

We are adding an additional step to our onboarding process (Code mapping). The content is already developed and needs to be updated on the front-end.

What you need to know

• Content updates doc: Use a source of truth for content changes.
• Figma reference: Reference for components only (i.e. NOT content).

Acceptance criteria

• New Map your codes section is added
• Subsequent section numbers are updated
• Create hash-links for each numbered section

To do

• When making PR, tag @jillian-hammer as a reviewer