Update docs/how_to_guides.rst

Co-authored-by: Will Barnes <will.t.barnes@gmail.com>

docs/how_to_guides.rst

@@ -77,7 +77,9 @@ rebuilt by running the following code in python:
 .. code-block:: pycon
 
    >>> import fiasco
-   >>> fiasco.util.build_hdf5_dbase(fiasco.defaults['ascii_dbase_root'], fiasco.defaults['hdf5_dbase_root'], overwrite=True)  # doctest: +SKIP
+   >>> fiasco.util.build_hdf5_dbase(fiasco.defaults['ascii_dbase_root'], 
+                                    fiasco.defaults['hdf5_dbase_root'], 
+                                    overwrite=True)  # doctest: +SKIP
 
 which will overwrite the old HDF5 file (if any) with a new version.  The arguments of the function can alternatively point to your preferred location(s),
 rather than just using the default values.