Change: Rename the Manual navigation button to Wiki (#350)

Author: J-PIE-314

_layouts/default.html

@@ -58,7 +58,7 @@
                 <li class="{% if page.active_nav == 'about' %}selected{% endif %}">
                     <a href="{{ site.baseurl }}/about.html">About</a>
                 </li>
-                <li><a href="https://wiki.openttd.org/">Manual</a></li>
+                <li><a href="https://wiki.openttd.org/">Wiki</a></li>
                 <li class="{% if page.active_nav == 'screenshots' or layout.active_nav == 'screenshots' %}selected{% endif %}">
                     <a href="{{ site.baseurl }}/screenshots.html">Screenshots</a>
                 </li>