[roll third_party/pigweed] docs: Clarify control flow C++ style

Add a section clarifying expected control flow style; in particular,
that early return and continue is preferred over right-creeping
functions and loops.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/97806

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 36c56d1d47415d5..19f3a3d1077c6fc
Roller-URL: https://ci.chromium.org/b/8811429753661261105
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8811429753661261105
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ib3b740bbe20371e0d008cc65644be863f3984382
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/97949
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 36c56d1..19f3a3d 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 36c56d1d47415d5192c95049796aa1bf58caf1f9
+Subproject commit 19f3a3d1077c6fcccbd527a5aced0e8c4c02f6ab