Auto merge of #3392 - matklad:patch-1, r=steveklabnik

Add explanatory comment to header.html

See #3387

Author: bors

src/doc/header.html

@@ -27,6 +27,7 @@ <h1>CARGO</h1>
                 Docs
                 <span class="arrow"></span>
             </button>
+            <!-- Sync this list with https://github.com/rust-lang/crates.io/blob/master/app/templates/application.hbs -->
             <ul id="current-user-links" class="dropdown" data-bindattr-503="503">
                 <li><a href='index.html'>Getting Started</a></li>
                 <li><a href='guide.html'>Guide</a></li>