Modified version of https://github.com/thesoftwarebin/the-emacs-software-bin/blob/master/teletype.el

gistfile1.el

(defun teletype-char (c short-pause long-pause)
  (let ((med-pause (/ (+ long-pause (* 2 short-pause)) 3.0)))
    (cond 
     ((equal c ?.)
      (insert (char-to-string c))
      (sit-for long-pause))
     ((equal c ?,)
      (insert (char-to-string c))
      (sit-for med-pause))
     ((equal c ?\n)
      (sit-for med-pause) (insert (char-to-string c))
      (sit-for med-pause))
     (t
      (insert (char-to-string c))
      (sit-for short-pause)))))

(defun teletype-text (str short-pause long-pause)
  (mapcar 
   (lambda (strchar) 
     (teletype-char strchar short-pause long-pause))
   (string-to-list str)))

(defun teletype-demo (pause-between-keys pause-between-rows buffer-title text)
  "Print characters with a pause between each character."
  (switch-to-buffer (get-buffer-create buffer-title))
  (erase-buffer)
  (teletype-text text pause-between-keys pause-between-rows))

(defun teletype-run-demo ()
  "Demonstrate teletyping."
  (interactive)
  (teletype-demo 
   0.1 
   0.5 
   "Emacs teletype demo" 
   (concat
    "Hello Emacs user,\n\n"
    "  teletype-like printing can be useful to\n"
    "keep the user focused on a brief tutorial.\n\n"
    "  You are currently reading at 10 cps, with\n"
    "pauses of 0.5 sec at punctuation and newlines.\n"
    "  If this demo annoys you, stop it with C-g.\n\n"
    "  To run your own demo, you may load teletype.el and\n"
    "execute the following LISP function:\n\n"
    "  (teletype-demo 0.1 0.5 demo-title all-your-text)\n\n"
    "Future improvements could be:\n\n"
    "  - read text from file\n"
    "  - a resumable \"pause\" key\n"
    "  - support for text coloring\n"
    "  - support for typewriter sound (tick-tick-tick)\n"
    "  - configurable regexps for pauses (so for example you\n"
    "    don't have to ... wait so long at the ellipsys\n"
    "    triple dots)\n\n"
    "  Hope you enjoyed, regards.\n\n"
    "        The Software Bin\n"
    "  http://github.com/thesoftwarebin\n")))