I'm sorry, I should have said it before. Make sure you are out of PHP mode when you add that line. Anything between the <?php?> tags is supposed to be PHP code and anything outside of the tags is treated as regular HTML.
Imagine this, you rename an HTML(page.html) page to php(page.php) and do not even change the file. No, <?php?> tags, just the same HTML page. It will render exactly the same as if it were named .html.
So, just look for the <head> section of the page and add the line in there. If you don't see a head section, then the file you are viewing is probably being included from a master file which does have the <head> section.