song: document get_song_url()

[merged r7184 from branches/ew]

git-svn-id: https://svn.musicpd.org/mpd/trunk@7242 09075e82-0dd4-0310-85a5-a0d7c8717e4f

src/song.h

@@ -71,6 +71,12 @@ int updateSongInfo(Song * song);
 
 void printSongUrl(int fd, Song * song);
 
+/*
+ * get_song_url - Returns a path of a song in UTF8-encoded form
+ * path_max_tmp is the argument that the URL is written to, this
+ * buffer is assumed to be MPD_PATH_MAX or greater (including
+ * terminating '\0').
+ */
 char *get_song_url(char *path_max_tmp, Song * song);
 
 #endif