feat: port Archive.Wiedijk100Theorems.BallotProblem (leanprover-community#5204)

Co-authored-by: Moritz Firsching <firsching@google.com>

Author: int-y1

Archive.lean

@@ -27,6 +27,7 @@ import Archive.Imo.Imo2020Q2
 import Archive.Imo.Imo2021Q1
 import Archive.Wiedijk100Theorems.AreaOfACircle
 import Archive.Wiedijk100Theorems.AscendingDescendingSequences
+import Archive.Wiedijk100Theorems.BallotProblem
 import Archive.Wiedijk100Theorems.BirthdayProblem
 import Archive.Wiedijk100Theorems.CubingACube
 import Archive.Wiedijk100Theorems.FriendshipGraphs