[roll third_party/pigweed] pw_unit_test: Update docs

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/193671

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: dc5ef2e7790bfa5..aaf126b137a6c24
Roller-URL: https://ci.chromium.org/b/8754184717682951985
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Id1b4f05fe683ba06229be9d073b853208e4f6dcd
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/195116
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 dc5ef2e..aaf126b 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit dc5ef2e7790bfa526901e3de3ef41f43b48fb823
+Subproject commit aaf126b137a6c24d03ef0a07d5d8de998f54dbce