adding googleplus button to my custom theme

I have a custom theme which had google plus missing so cant enable that, instead i have to find a place to add a code and dont know where to place it, have tried in footer.php nothing happens, i also have sociallinks_footer.php all the links are there for existing one and nothing happens either, any help would be great, btw the code i been told to use is:

<!– Place this tag in your head or just before your close body tag. –>
<script src=”https://apis.google.com/js/platform.js&#8221; async defer></script>

<!– Place this tag where you want the +1 button to render. –>
<div class=”g-plusone” data-size=”medium” data-annotation=”none” data-href=”https://plus.google.com/+ZENITHACCOMMODATION/posts”></div&gt;