Move style guide and abseil-in-webrtc into g3doc subfolder

No-Try: true
Bug: None
Change-Id: I45c3e515f6e446f8982333869d8ad2c6ae15978d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/218347
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Artem Titov <titovartem@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34004}
diff --git a/api/README.md b/api/README.md
index 4cc7993..7c1a27f 100644
--- a/api/README.md
+++ b/api/README.md
@@ -1,6 +1,6 @@
 # How to write code in the `api/` directory
 
-Mostly, just follow the regular [style guide](../style-guide.md), but:
+Mostly, just follow the regular [style guide](../g3doc/style-guide.md), but:
 
 * Note that `api/` code is not exempt from the “`.h` and `.cc` files come in
   pairs” rule, so if you declare something in `api/path/to/foo.h`, it should be
@@ -17,7 +17,7 @@
 
 For headers in `api/` that need to refer to non-public types, forward
 declarations are often a lesser evil than including non-public header files. The
-usual [rules](../style-guide.md#forward-declarations) still apply, though.
+usual [rules](../g3doc/style-guide.md#forward-declarations) still apply, though.
 
 `.cc` files in `api/` should preferably be kept reasonably small. If a
 substantial implementation is needed, consider putting it with our non-public