content/static: add readme headings to the sidenav

This change adds the readme headings to the outline
in the sidenav and unifies the navigation tree into
a single accessible structure.

Styles within the tree are based on the accessiblity
tree structure. This will make it easier to see when
updates to the tree are inserted incorrectly because
they'll be matched by visual breakages on the page.

Sidenav and readme click handlers are updated to
ensure that when an outline item is clicked the
corresponding content is visible.

Change-Id: Ie6062c24f37bec9fffe242aa1398ec815606c613
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/271319
Trust: Jamal Carvalho <jamal@golang.org>
Run-TryBot: Jamal Carvalho <jamal@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Julie Qiu <julie@golang.org>

0 files changed, 0 insertions, 0 deletions