Update lb_radio.rst

The next section lists 7 different entities that are supported, not just artist and tag.

docs/lb_radio.rst

@@ -19,7 +19,7 @@ what music should be added to the playlist. A Radio prompt is composed of one or
 
 
 Each term generates a stream of recordings and recordings from each of the streams are then interleaved to make a single playlist.
-The entity must be either "artist" or "tag" currently. The optional weight argument allows the user to control how often this term
+The optional weight argument allows the user to control how often this term
 will contribute to the final playlist. By default each term gets a value of 1, if the user didn't specify a weight value.
 A term with a weight of 3 will contribute 3 times more recordings than a term with weight 1. The final part of each term
 are options, documented in the options section.