roll: third_party/pigweed: docs: Update Sense flashing instructions

* Explain how to troubleshoot the inaccessible serial number issue.
* Move interactive prompt selection content to appendix.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/229608
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 63604e695b9f10f..56ac0e66cadfd5d
Roller-URL: https://ci.chromium.org/b/8739581897898554465
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I1a5e866cb524665ced3ee447988f00262f45b17f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/229931
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
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 63604e6..56ac0e6 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 63604e695b9f10f4e869732d90efd8d6b5d5fa7d
+Subproject commit 56ac0e66cadfd5d5c157a5931801cb55babbafb9