Docs: Include a course link in the header

Author: tpoole

docs/doxygen/header.html

@@ -71,6 +71,7 @@
     <li id="menu-item-291" class="menu-item menu-item-type-custom menu-item-object-custom menu-item-has-children menu-item-291"><a href="https://juce.com/learn/documentation/">Learn</a>
     <ul class="sub-menu">
         <li id="menu-item-241" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-241"><a href="https://juce.com/learn/documentation/">Documentation</a></li>
+        <li id="menu-item-4588" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-4588"><a href="https://juce.com/learn/course/">Course</a></li>
         <li id="menu-item-240" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-240"><a href="https://juce.com/learn/tutorials/">Tutorials</a></li>
         <li id="menu-item-275" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-275"><a href="https://juce.com/stories/">Made with JUCE</a></li>
         <li id="menu-item-242" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-242"><a href="https://juce.com/resources/">Resources</a></li>