For #350, add a long-term TODO item

TODO.rst

@@ -95,6 +95,12 @@ Adding more smarts to ephemeris handling
 * And additionally: the error when not enough bodies are available for
   deflection maybe someday needs to be more helpful.
 
+* Bring support for Type 1 and Type 21 JPL ephemerides into Skyfield
+  from the third-party libraries where it now lives.  The routines will
+  need to be vectorized and updated to use a Skyfield approach to vector
+  and matrix operations.  When complete and documented, make a comment
+  at: https://github.com/skyfielders/python-skyfield/issues/350
+
 For 2.0
 =======
 

skyfield/documentation/planets.rst

@@ -218,8 +218,8 @@ at the completion of a ``with`` statement:
 
 .. _third-party-ephemerides:
 
-Third-party libraries for other ephemeris formats
-=================================================
+Type 1 and Type 21 ephemeris formats
+====================================
 
 If you generate an ephemeris with a tool like NASA’s
 `HORIZONS <https://ssd.jpl.nasa.gov/horizons.cgi>`_ system,