[roll third_party/pigweed] pw_boot: Update status and general doc cleanup

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/189298

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: b63b498bfa32e6f..9d700d34f4a9625
Roller-URL: https://ci.chromium.org/b/8757275870537495553
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I270a946a1ef03f2fa9aade4e659ba9deb897c6b4
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/189947
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index b63b498..9d700d3 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit b63b498bfa32e6fce2134a7637d39c6cfd63a7b7
+Subproject commit 9d700d34f4a96257ea96eb2b37ae66883a810aea