Add ruby example

Ruby/xor.rb

@@ -0,0 +1,15 @@
+def encryptDecrypt(string)
+    key = ['K', 'C', 'Q']
+    result = ""
+    codepoints = string.each_codepoint.to_a
+    codepoints.each_index do |i|
+        result += (codepoints[i] ^ key[i % key.size].ord).chr
+    end
+    result
+end
+
+encrypted = encryptDecrypt("kylewbanks.com")
+puts "Encrypted: #{encrypted}"
+
+decrypted = encryptDecrypt(encrypted)
+puts "Decrypted: #{decrypted}"