Fix set_voice => set_voices

docs/CONFIG-README

@@ -77,7 +77,7 @@ All the different options are listed below.
 Other examples:
 <set lang='EN'>
 <set bgcolor="#dedeee" text="black" hbgcolor="#666699" hcolor="white" hicell="#BABADD" hicell2="#CCCCCC">
-<set show_voice="1" show_wpl="1">
+<set show_voices="1" show_wpl="1">
 <set topichistory="3" timeoffset="+0">
 
 There is many options which can be set, here is a list of them all (not