Gitiles navigation bar

Change-Id: I739beb6a30a474fe7bd9b8726cb0829172a307a3
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/19860
Reviewed-by: Takuto Ikuta <tikuta@google.com>
Commit-Queue: Takuto Ikuta <tikuta@google.com>

navbar.md

diff --git a/navbar.md b/navbar.md
new file mode 100644
index 0000000..6f8c205
--- /dev/null
+++ b/navbar.md
@@ -0,0 +1,9 @@
+# GN
+
+* [Home][home]
+* [Quick Start](/docs/quick_start.md)
+* [FAQ](/docs/faq.md)
+* [Reference](/docs/reference.md)
+* [Style Guide](/docs/style_guide.md)
+
+[home]: /README.md