DOC: Add download link for executed .ipynb file

Author: mgeier

doc/conf.py

@@ -50,6 +50,7 @@
       <a class="reference external" href="https://github.com/spatialaudio/nbsphinx/blob/{{ env.config.release|e }}/{{ docname|e }}">{{ docname|e }}</a>.
       Interactive online version:
       <span style="white-space: nowrap;"><a href="https://mybinder.org/v2/gh/spatialaudio/nbsphinx/{{ env.config.release|e }}?filepath={{ docname|e }}"><img alt="Binder badge" src="https://mybinder.org/badge_logo.svg" style="vertical-align:text-bottom"></a>.</span>
+      <a href="{{ env.docname.split('/')|last|e + '.ipynb' }}" class="reference download internal" download>Download notebook</a>.
       <script>
         if (document.location.host) {
           let nbviewer_link = document.createElement('a');
@@ -59,7 +60,7 @@
             window.location.host +
             window.location.pathname.slice(0, -4) +
             'ipynb');
-          nbviewer_link.innerHTML = 'View in <em>nbviewer</em>';
+          nbviewer_link.innerHTML = 'Or view it on <em>nbviewer</em>';
           nbviewer_link.classList.add('reference');
           nbviewer_link.classList.add('external');
           document.currentScript.replaceWith(nbviewer_link, '.');