You can access the HEAD section from the Edit Webmaster Verification window in the Website screen.
To add a favicon to your site, add the required HTML code in this dialog window. Please note that the favicon image should be hosted externally (or if uploading a template can be included in the Images directory).
When adding a favicon, please use the following format (dependent on the image file format):
<link rel="icon" type="image/vnd.microsoft.icon" href="path-to/favicon.ico">
<link rel="icon" type="image/png" href="path-to/name-favicon-ico.png">
<link rel="icon" type="image/gif" href="path-to/name-gif-file.gif">