docs: Add a doc for D-Bus MojoConnectionService Provider

To increase the doc (go/mojo_connection_service) and the service
provider's visibility, this commit adds a doc in Chromium

BUG=b:175283521
TEST=viewed the md on Google Chrome locally

Change-Id: Ic9ceaecae0699bc2441a6cecf983f5fd156a48e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2583676
Commit-Queue: Cheng-Hao Yang <chenghaoyang@chromium.org>
Reviewed-by: Mike Pinkerton <pinkerton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#858517}
diff --git a/docs/README.md b/docs/README.md
index e6fb53d..a63cd425 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -396,6 +396,8 @@
     patterns for practical IPC conversion work
 *   [Mojo “Style” Guide](security/mojo.md) - Recommendations for best practices
     from Mojo and IPC reviewers
+*   [D-Bus Mojo Connection Service](dbus_mojo_connection_service.md) - A service
+    in Chrome to bootstrap CrOS services' Mojo connection.
 
 ### Speed
 *   [Chrome Speed](speed/README.md) - Documentation for performance measurements and regressions in Chrome.