DOC: Add instructions to install pandoc

Closes #72.

doc/usage.jupyter

@@ -23,6 +23,19 @@ markdown
     Recent versions of Python already come with `pip` pre-installed.
     If you don't have it, you can [install it manually](https://pip.pypa.io/en/latest/installing/).
 
+    ### pandoc
+
+    The stand-alone program [pandoc](http://pandoc.org/) is used to convert Markdown content to something Sphinx can understand. You have to install this program separately, ideally with your package manager. If you are using `conda`, you can select the [conda-forge](https://conda-forge.github.io/) channel to install the [pandoc](https://anaconda.org/conda-forge/pandoc) package.
+    If that doesn't work out for you, have a look at `pandoc`'s [installation instructions](http://pandoc.org/installing.html).
+
+    <div class="alert alert-info">
+
+    **Note:**
+
+    The use of `pandoc` in `nbsphinx` is temporary, but will likely stay that way for a long time, see [issue #36](https://github.com/spatialaudio/nbsphinx/issues/36).
+
+    </div>
+
     ### Syntax Highlighting
 
     To get proper syntax highlighting in code cells, you'll need an appropriate *Pygments lexer*.