updating DIRECTORY.md

Author: cclauss

DIRECTORY.md

@@ -146,6 +146,7 @@
   * [Baconian Cipher](ciphers/baconian_cipher.py)
   * [Base16](ciphers/base16.py)
   * [Base32](ciphers/base32.py)
+  * [Base58](ciphers/base58.py)
   * [Base64 Cipher](ciphers/base64_cipher.py)
   * [Base85](ciphers/base85.py)
   * [Beaufort Cipher](ciphers/beaufort_cipher.py)