docs: Render example TSV files as tables and provide download links

This makes the TSV examples more readable on the page (i.e. the columns
line up unlike the raw TSV) while still retaining the ability for a
reader to get a copy of the example file to tinker with.

We could use the tab-width option of the literalinclude directive to
line up the columns, but that would break the ability to copy/paste the
contents into a new TSV file, as the tabs get expanded to spaces when
tab-width is used.

docs/advanced-functionality/drag-drop-csv-tsv.rst

@@ -10,20 +10,26 @@ The general format is compatible with other popular tools such as `MicroReact <h
 Example:
 --------
 
-A TSV file as follows can be dragged onto `nextstrain.org/zika <https://nextstrain.org/zika>`__ to add a "secret" color-by:
+A :download:`small TSV file <../assets/extra-data.tsv>` with the following data:
 
-.. literalinclude:: ../assets/extra-data.tsv
-   :language: text
+.. csv-table::
+   :file: ../assets/extra-data.tsv
+   :delim: tab
+
+can be dragged onto `nextstrain.org/zika <https://nextstrain.org/zika>`_ to add a "secret" color-by:
 
 .. figure:: ../assets/extra-data.png
    :alt: Auspice with extra data shown via TSV
 
    Auspice with extra data shown via TSV
 
-A more complex metadata file may look like the following, which makes use of additional features available. This defines colours for the metadata (e.g. ``A`` is yellow, ``B`` is orange) as well as associating strains with (made up) geographic coordinates.
+A :download:`more complex TSV file <../assets/extra-data-2.tsv>` can add more data to make use of additional features available:
+
+.. csv-table::
+   :file: ../assets/extra-data-2.tsv
+   :delim: tab
 
-.. literalinclude:: ../assets/extra-data-2.tsv
-   :language: text
+This defines colours for the metadata (e.g. ``A`` is yellow, ``B`` is orange) as well as associating strains with (made up) geographic coordinates.  When dragged onto `nextstrain.org/zika`_, it looks like:
 
 .. figure:: ../assets/extra-data-2.png
    :alt: Auspice with extra data shown via TSV