Adding a little more Python documentation.

source/python/README.md

@@ -12,3 +12,27 @@ Observer(self, latitude, longitude, height=0)
 ```
 Represents the geographic location of an observer on the surface of the Earth.
 
+:param latitude: Geographic latitude in degrees north of the equator.
+:param longitude: Geographic longitude in degrees east of the prime meridian at Greenwich, England.
+:param height: Elevation above sea level in meters.
+
+## GeoMoon
+```python
+GeoMoon(time)
+```
+Calculates the geocentric position of the Moon at a given time.
+
+Given a time of observation, calculates the Moon's position as a vector.
+The vector gives the location of the Moon's center relative to the Earth's center
+with x-, y-, and z-components measured in astronomical units.
+
+This algorithm is based on Nautical Almanac Office's <i>Improved Lunar Ephemeris</i> of 1954,
+which in turn derives from E. W. Brown's lunar theories from the early twentieth century.
+It is adapted from Turbo Pascal code from the book
+[Astronomy on the Personal Computer](https://www.springer.com/us/book/9783540672210)
+by Montenbruck and Pfleger.
+
+:param time:  The date and time for which to calculate the Moon's position.
+:return The Moon's position as a vector in J2000 Cartesian equatorial coordinates.
+:rtype Vector
+