styleguide: Fix/clarify the cbegin/cend rules are for container methods

styleguide/c++/c++11.html

Index: styleguide/c++/c++11.html
diff --git a/styleguide/c++/c++11.html b/styleguide/c++/c++11.html
index 8c3cbc0426634f5be32e0a81cdbeeddda577b3ba..ef0268492b0892e961b1bc64b947401f20d416a8 100644
--- a/styleguide/c++/c++11.html
+++ b/styleguide/c++/c++11.html
@@ -807,10 +807,10 @@ the <code>&lt;complex&gt;</code> library.</td>
 
 <tr>
 <td>Constant Iterator Methods on Containers</td>
-<td><code>std::cbegin()</code> and <code>std::cend()</code></td>
+<td><code>std::vector::cbegin()</code> and <code>std::vector::cend()</code></td>
 <td>Enforces iteration methods that don't change container contents</td>
-<td>TODO: documentation link</td>
-<td></td>
+<td><a href="http://en.cppreference.com/w/cpp/container/vector/begin">std::vector::cbegin<a></td>
+<td>This applies to all containers, std::vector is just an example. <a href="https://groups.google.com/a/chromium.org/d/topic/cxx/cS83F_buqLM/discussion">Discussion thread</a></td>
 </tr>
 
 <tr>