README example needs another couple of imports

I needed to add `all` and `tempo` to the list of imports from `leipzig.melody` when running the example code.

README.md

@@ -42,7 +42,7 @@ ways of manipulating this basic structure, but there's nothing to stop you from
 You can create a melody with the `phrase` function. Here's a simple melody:
 
 ```clojure
-(require '[leipzig.melody :refer [bpm is phrase then times where with]])
+(require '[leipzig.melody :refer [all bpm is phrase tempo then times where with]])
 
 (def melody
          ; Row,  row,  row   your  boat