Update docs/scarpet/api/Scoreboard.md

Co-authored-by: gnembon <41132274+gnembon@users.noreply.github.com>

docs/scarpet/api/Scoreboard.md

@@ -12,7 +12,7 @@ With specified `objective` and
 
 Adds a new objective to scoreboard. If `criterion` is not specified, assumes `'dummy'`.
 If the objective already exists, changes the criterion of that objective and returns false.
-If the objective was added, returns true.
+If the objective was added, returns `true`. If nothing is affected, returns `null`
 
 <pre>
 scoreboard_add('counter')
@@ -163,4 +163,3 @@ for(bossbar(),bossbar(_,'remove'))  -> remove all bossbars
 
 
 
-