Replace c++11.html with c++11.md.

This removes the dependency on chromium-cpp.appspot.com to serve the
modern C++/Abseil style guide. It changes the formatting from a set of
tables to a list of features in sub-headings since gitiles markdown's
table support is limited.

Bug: 1243839
Change-Id: Id34d58d0c7178db5802fff06695836c83d7afc06
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3123974
Commit-Queue: Joe Mason <joenotcharles@google.com>
Auto-Submit: Joe Mason <joenotcharles@google.com>
Reviewed-by: Joey Arhar <jarhar@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: Mirko Bonadei <mbonadei@chromium.org>
Cr-Commit-Position: refs/heads/main@{#921667}
NOKEYCHECK=True
GitOrigin-RevId: fe4f25628dd87832efa81ed0c309ff4d57b325a4

README.chromium

diff --git a/README.chromium b/README.chromium
index 2e84079..0c6a6a8 100644
--- a/README.chromium
+++ b/README.chromium
@@ -9,9 +9,10 @@
 
 Description:
 This directory contains the source code of Abseil for C++. This can be used by
-Chromium, subject to the guidance at https://chromium-cpp.appspot.com/; it can
-be used without restriction by Chromium's dependencies, except that objects
-compiled into Chromium itself cannot use anything relying on
+Chromium, subject to the guidance at
+https://chromium.googlesource.com/chromium/src/+/main/styleguide/c++/c++11.md;
+it can be used without restriction by Chromium's dependencies, except that
+objects compiled into Chromium itself cannot use anything relying on
 absl::base_internal::FastTypeId (see https://crbug.com/1096380).
 
 How to update Abseil: