[roll third_party/pigweed] pw_software_update: docs: update systems overview

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/95368

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 6c0716d7fb60f18..65193ef8c79f5ca
Roller-URL: https://ci.chromium.org/b/8813667079108084721
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8813667079108084721
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ib0e9e079e972ed9404066d458f781c6717f6f0e8
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/95412
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
1 file changed