adds Rust favicon
<meta name="description" content="The Rust toolchain installer">
<link rel="stylesheet" href="normalize.css">
<link rel="stylesheet" href="rustup.css">
+ <link rel="icon" type="image/png" sizes="32x32" href="https://www.rust-lang.org/static/images/favicon-32x32.png">
+ <link rel="icon" type="image/svg+xml" href="https://www.rust-lang.org/static/images/favicon.svg">
+ <link rel="mask-icon" href="https://www.rust-lang.org/static/images/safari-pinned-tab.svg" color="#000">
</head>
