fix: expand builds section description

docs/src/tutorial/custom-data.rst

@@ -104,10 +104,10 @@ This is the same as the previous file, with some additions:
 1. A second input for the custom data, referencing the metadata and sequences files downloaded from GISAID.
 2. A ``builds`` section that defines one output :term:`docs.nextstrain.org:dataset` using:
 
-   1. A custom name ``custom-build``
-   2. A custom title ``Build with custom data and example data``
-   3. A pre-defined subsampling scheme ``all`` (TODO: add doc link)
-   4. An Auspice config file with the contents:
+   1. A custom name ``custom-build``, which will be used to create the dataset filename, in this case ``auspice/ncov_custom-build.json``.
+   2. A custom title ``Build with custom data and example data``, which will be shown when you visualize the dataset in Auspice.
+   3. A pre-defined subsampling scheme ``all``, which tells the workflow to skip subsampling. (TODO: add doc link)
+   4. An Auspice config file, ``ncov-tutorial/auspice-config-custom-data.json``, which defines various parameters for how the data should be visualized in Auspice. It has the following contents:
 
       .. code-block:: json