Sync Lock: Clarify that Mixxx will override the user's choice in some…

… circumstances.

source/chapters/djing_with_mixxx.rst

@@ -149,7 +149,7 @@ eject, load, and queue any track with sync lock and it won't interrupt the
 playback of the other decks.  However, changing the rate of a stopped deck will
 change the rate of playing decks.
 
-Syn Lock will also notice if one of your tracks is double the BPM of another
+Sync Lock will also notice if one of your tracks is double the BPM of another
 track and match them correctly.  So if you want to mix a 140 BPM drum & bass
 track with a 70 bpm dubstep track, Sync Lock will make sure they are lined up
 properly.
@@ -200,6 +200,11 @@ the following transition. If you'd like to use the the tempo from the intro of t
 track instead, click the Leader (Crown) button of its deck.
 The deck then becomes the soft leader, and Mixxx will use that deck's tempo instead.
 
+The only case when a stopped deck can be a Leader is if no other deck is
+playing. Once a deck starts playing, Mixxx will pick that as the leader instead.
+If another deck starts playing, then you will be able to pick which one you want
+to be the leader again.
+
 If you'd prefer a steady tempo during transitions like in Mixxx before Version 2.4,
 you may select :guilabel:`Use steady Tempo` for :guilabel:`Sync mode` in the
 :guilabel:`Decks` preferences. In this mode all decks become a follower during a