roll: third_party/pigweed pw_kernel: Add more early draft docs

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/297173
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Original-Revision: 899c24a93a7a0c411d374f3bd202489428df2036

Rolled-Repo: https://pigweed.googlesource.com/pigweed/pigweed
Rolled-Commits: 3f4f714a9366b6..899c24a93a7a0c
Roll-Count: 1
Roller-URL: https://cr-buildbucket.appspot.com/build/8712203969697873105
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I71faa8e131f96b63591d68e17f2c466f4fd428ad
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/298072
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
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diff --git a/third_party/pigweed b/third_party/pigweed
index 3f4f714..899c24a 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 3f4f714a9366b6aca570d4e2fd20857642a3da40
+Subproject commit 899c24a93a7a0c411d374f3bd202489428df2036