Fix issue with link to GitHub from RMarkdown files

Jekyll doesn't export the _episodes_rmd so we need to flag the files.
Each Rmd file must have in the YAML header

    source: Rmd

Author: rgaiacs

_includes/lesson_footer.html

@@ -17,7 +17,13 @@ <h4>
     </div>
     <div class="col-md-6" align="right">
       <h4>
+	{% if page.source %}
+	{% if page.source == "Rmd" %}
+	<a href="{{site.github.repository_url}}/edit/gh-pages/{{page.path|replace: "_episodes", "_episodes_rmd" | replace: ".md", ".Rmd"}}">Edit on GitHub</a>
+	{% endif %}
+	{% else %}
 	<a href="{{site.github.repository_url}}/edit/gh-pages/{{page.path}}">Edit on GitHub</a>
+	{% endif %}
 	/
 	<a href="{{ site.github.repository_url }}/blob/gh-pages/CONTRIBUTING.md">Contributing</a>
 	/

_includes/navbar.html

@@ -76,7 +76,13 @@
 
 	{% comment %} Always show license. {% endcomment %}
         <li><a href="{{ page.root }}/license/">License</a></li>
+	{% if page.source %}
+	{% if page.source == "Rmd" %}
+	<li><a href="{{site.github.repository_url}}/edit/gh-pages/{{page.path|replace: "_episodes", "_episodes_rmd" | replace: ".md", ".Rmd"}}">Improve this page <span class="glyphicon glyphicon-pencil" aria-hidden="true"></span></a></li>
+	{% endif %}
+	{% else %}
 	<li><a href="{{site.github.repository_url}}/edit/gh-pages/{{page.path}}">Improve this page <span class="glyphicon glyphicon-pencil" aria-hidden="true"></span></a></li>
+	{% endif %}
       </ul>
       <form class="navbar-form navbar-right" role="search" id="search" onsubmit="google_search(); return false;">
         <div class="form-group">