Adding comments on include files purposes

_includes/carpentries.html

+{% comment %}
+  General description of Software and Data Carpentry.
+{% endcomment %}
 <div class="row">
   <div class="col-md-2" align="center">
     <a href="{{ site.swc_site }}"><img src="{{ page.root }}/assets/img/swc-icon-blue.svg" alt="Software Carpentry logo" /></a>
@@ -23,5 +26,3 @@
     building on learners' existing knowledge to enable them to quickly apply skills learned to their own research.
   </div>
 </div>
-
-

_includes/episode_keypoints.html

+{% comment %}
+  Display key points for an episode.
+{% endcomment %}
 <blockquote class="keypoints">
   <h2>Key Points</h2>
   <ul>

_includes/javascript.html

+{% comment %}
+  Javascript used in lesson and workshop pages.
+{% endcomment %}
 <script src="{{ page.root }}/assets/js/jquery.min.js"></script>
 <script src="{{ page.root }}/assets/js/bootstrap.min.js"></script>
 <script src="{{ page.root }}/assets/js/lesson.js"></script>

_includes/lesson_footer.html

+{% comment %}
+  Footer for lesson pages.
+{% endcomment %}
 <footer>
   <div class="row">
     <div class="col-md-6" align="left">

_includes/main_title.html

+{% comment %}
+  Main title for lesson pages.
+{% endcomment %}
 <h1 class="maintitle"><a href="{{ page.root }}/">{{ site.title }}</a>{% if page.title %}: {{ page.title }}{% endif %}</h1>

_includes/navbar.html

+{% comment %}
+  Lesson navigation bar.
+{% endcomment %}
 <nav class="navbar navbar-default">
   <div class="container-fluid">
     <div class="navbar-header">

_includes/workshop_ad.html

+{% comment %}
+  Advertising box at the top of a workshop website home page.
+{% endcomment %}
 <div class="jumbotron">
   <div class="row">
     <div class="col-md-10 col-md-offset-1">

_includes/workshop_footer.html

+{% comment %}
+  Footer for a standard workshop.
+{% endcomment %}
 <footer>
   <div class="row">
     <div class="col-md-6" align="left">