[docs] Add navbar to top-level chromium docs

To make navigation easier when viewing docs generated by gitiles. The navbar is similar to [ChromiumOS][1]'s one.

Please preview the change at [2].


[1]:
https://source.chromium.org/chromiumos/chromiumos/codesearch/+/main:docs/navbar.md
[2]: https://chromium.googlesource.com/chromium/src/+/refs/changes/43/3771143/5/docs/README.md

Change-Id: If2724dc7ef222dfc1e34b1804da017e3fdd26516
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3771143
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Commit-Queue: Ming-Ying Chung <mych@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1025610}

docs/README.md

@@ -1,22 +1,30 @@
 # Chromium docs
 
-This directory contains chromium project documentation in
-[Gitiles-flavored Markdown].  It is automatically [rendered by Gitiles].
+This directory contains [chromium project](https://www.chromium.org/Home/)
+documentation in [Gitiles-flavored Markdown]. It is automatically
+[rendered by Gitiles].
 
 [Gitiles-flavored Markdown]: https://gerrit.googlesource.com/gitiles/+/master/Documentation/markdown.md
 [rendered by Gitiles]: https://chromium.googlesource.com/chromium/src/+/main/docs/
 
-If you add new documents, please also add a link to them in the Document Index
-below.
+**If you add new documents, please also add a link to them in the Document Index
+below.**
 
 [TOC]
 
 ## Creating Documentation
 
-Markdown documents must follow the
-[style guide](https://github.com/google/styleguide/tree/gh-pages/docguide).
+### Guidelines
 
-### Preview local changes using [md_browser](../tools/md_browser/)
+*   See the [Chromium Documentation Guidelines](/documentation_guidelines.md)
+    and the
+    [Chromium Documentation Best Practices](/documentation_best_practices.md).
+*   Markdown documents must follow the
+    [style guide](https://github.com/google/styleguide/tree/gh-pages/docguide).
+
+### Previewing changes
+
+#### Locally using [md_browser](../tools/md_browser/)
 
 ```bash
 # in chromium checkout
@@ -25,7 +33,7 @@ Markdown documents must follow the
 
 This is only an estimate. The **gitiles** view may differ.
 
-### Review changes online with gerrit's links to gitiles
+#### Online with Gerrit's links to gitiles
 
 1.  Upload a patch to gerrit, or receive a review request.
     e.g. https://chromium-review.googlesource.com/c/3362532
@@ -37,7 +45,7 @@ This is only an estimate. The **gitiles** view may differ.
     -> Patchset 3
     [browse](https://chromium.googlesource.com/chromium/src/+/refs/changes/32/3362532/3/docs/README.md)
     | DOWNLOAD <br>
-    at the top left of the page. Click on the second 
+    at the top left of the page. Click on the second
     "[browse](https://chromium.googlesource.com/chromium/src/+/refs/changes/32/3362532/3/docs/README.md)"
     link to open the preview for the current patch set.
 

docs/navbar.md

@@ -0,0 +1,16 @@
+# Chromium Docs
+
+[logo]: https://chromium-review.googlesource.com/plugins/chromium-style/static/web/chromium_logo.png
+[home]: /docs/README.md
+
+* [Home][home]
+* [Sitemap](/docs/README.md#document-index)
+* [Getting Started](/docs/contributing.md)
+* [Testing](/docs/testing/testing_in_chromium.md)
+* [Design Docs](/docs/design/README.md)
+* [Contact](https://www.chromium.org/contact/)
+* [Bugs](https://www.chromium.org/for-testers/bug-reporting-guidelines/)
+* [Markdown Style Guide](https://github.com/google/styleguide/tree/gh-pages/docguide)
+* [Markdown Syntax](https://gerrit.googlesource.com/gitiles/+/HEAD/Documentation/markdown.md)
+* [Old Docs](https://www.chromium.org/Home/)
+* [Search](https://source.chromium.org/chromium/chromium/src/+/main:docs/)