[DOC] Tweaks for String#chars

Author: BurdetteLamar

doc/string/chars.rdoc

@@ -3,3 +3,6 @@ Returns an array of the characters in +self+:
   'hello'.chars     # => ["h", "e", "l", "l", "o"]
   'тест'.chars      # => ["т", "е", "с", "т"]
   'こんにちは'.chars # => ["こ", "ん", "に", "ち", "は"]
+  ''.chars          # => []
+
+Related: see {Converting to Non-String}[rdoc-ref:String@Converting+to+Non--5CString].