:doc: Fix custom character set.

Author: javiercejudo

README.md

@@ -68,7 +68,7 @@ rather than an integer. For example we can convert a base 10 number
 to another base 10 number using a different encoding.
 
 ```ruby
-base = [:Q, :W, :E, :R, :T, :Y, :U, :I, :O, :U]
+base = [:Q, :W, :E, :R, :T, :Y, :U, :I, :O, :P]
 
 "10".b(10).to_a(base)  #=> [:W, :Q]
 ```