You'd think BigCommerce would have a "menu manger" feature to allow editing of menu items through a GUI but alas they do not (probably to stop unwitting store owners from creating confusing menu structures).

Anyway I need to add a "Home" link to the Page Menu so to do this I had to add the following code to the PageMenu.html files AKA %%SNIPPET_PageMenu%%

<li class="First %%GLOBAL_ActivePageHomeClass%%">
<a href="%%GLOBAL_ShopPathNormal%%"><span>%%LNG_MainPage%%</span></a>
</li>