[roll third_party/pigweed] pw_tokenizer: Migrate get started content to guides.rst

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/153650

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 49e3fc69d9fc824..8fd5c5ba3b7f3d7
Roller-URL: https://ci.chromium.org/b/8776926394937223153
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I1431b0994fd229d876df4a3525eebc9112bc80a5
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/153691
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 49e3fc6..8fd5c5b 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 49e3fc69d9fc82468ec33d8b5e6b7305b8e69109
+Subproject commit 8fd5c5ba3b7f3d74354a089c283a06d0c4cd3f21