Update architecture diagram in content/README.md

Update the image for content the architecture diagram to more closely align with the one at https://www.chromium.org/developers/design-documents/cookbook/ , which includes //components. This is hopefully more accurate and reduces confusion.

Change-Id: I49ef7107c6b4caa7371f0d349dad70ccf04de680
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4685395
Reviewed-by: Charlie Reis <[email protected]>
Reviewed-by: Avi Drissman <[email protected]>
Commit-Queue: Patricia Alfonso <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1173695}