docs: Fix link to building_crosvm.md

BUG=None
TEST=mdbook build docs/book

Change-Id: I5331cb9fed056c8b57171ba3db4d5b2521e6995c
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/3782185
Auto-Submit: Dennis Kempin <denniskempin@google.com>
Commit-Queue: Dennis Kempin <denniskempin@google.com>
Tested-by: Dennis Kempin <denniskempin@google.com>
Commit-Queue: Keiichi Watanabe <keiichiw@chromium.org>
Reviewed-by: Keiichi Watanabe <keiichiw@chromium.org>
diff --git a/docs/book/src/integration/chromeos.md b/docs/book/src/integration/chromeos.md
index 2406b10..2cc91c6 100644
--- a/docs/book/src/integration/chromeos.md
+++ b/docs/book/src/integration/chromeos.md
@@ -63,7 +63,7 @@
 prefer to use standard cargo workflows used upstream.
 
 Just make sure to initialize git submodules (`git submodules update --init`), which is not done by
-repo. After that, you can use the workflows as outlined in [Building Crosvm](../building_crosvm)
+repo. After that, you can use the workflows as outlined in [Building Crosvm](../building_crosvm.md)
 **outside** of cros_sdk.
 
 Note: You can **not** build or test ChromeOS specific features this way.