Add the ditaa.jar converter to the contrib directory.

Thanks to Stathis Sideris for this great program an his permission to
bundle it.

contrib/README

@@ -40,3 +40,4 @@ SCRIPTS (shell, bash, etc.)
 
 dir2org.zsh          --- Org compatible fs structure output
 org2hpda	     --- Generate hipster pda style printouts from Org-mode
+lisp/ditaa.jar       --- ASCII to PNG converter by Stathis Sideris, GPL

doc/org.texi

@@ -9935,6 +9935,9 @@ Linking to VM/BBDB/Gnus was first inspired by @i{Tom Shannon}'s
 @item
 @i{Ilya Shlyakhter} proposed the Archive Sibling.
 @item
+@i{Stathis Sideris} wrote the @file{ditaa.jar} ASCII to PNG converter that is
+now packaged into Org's @file{contrib} directory.
+@item
 @i{Daniel Sinder} came up with the idea of internal archiving by locking
 subtrees.
 @item