[roll third_party/pigweed] docs: Consolidate contributing docs in site nav

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/155816

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 2c3d12c8ac0dac9..17684877853edeb
Roller-URL: https://ci.chromium.org/b/8775299922076426209
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I3003ed8801e42ae33454d662c3fc49a51dc49482
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/156351
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 2c3d12c..1768487 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 2c3d12c8ac0dac96b3d1dda7bd9e92b58493fa71
+Subproject commit 17684877853edebc0fc2f8cfb2a3cb92b667ce92