Add Notes and Warnings About Optional Dependencies (#3393)

examples/arbitrarycallbackdatabot.py

@@ -6,6 +6,10 @@
 
 For detailed info on arbitrary callback data, see the wiki page at
 https://github.com/python-telegram-bot/python-telegram-bot/wiki/Arbitrary-callback_data
+
+Note:
+To use arbitrary callback data, you must install PTB via
+`pip install python-telegram-bot[callback-data]`
 """
 import logging
 from typing import List, Tuple, cast

examples/passportbot.py

@@ -10,6 +10,9 @@ See https://telegram.org/blog/passport for info about what telegram passport is.
 See https://github.com/python-telegram-bot/python-telegram-bot/wiki/Telegram-Passport
  for how to use Telegram Passport properly with python-telegram-bot.
 
+Note:
+To use Telegram Passport, you must install PTB via
+`pip install python-telegram-bot[passport]`
 """
 import logging
 from pathlib import Path

examples/timerbot.py

@@ -16,6 +16,10 @@ Usage:
 Basic Alarm Bot example, sends a message after a set time.
 Press Ctrl-C on the command line or send a signal to the process to stop the
 bot.
+
+Note:
+To use arbitrary callback data, you must install ptb via
+`pip install python-telegram-bot[callback-data]`
 """
 
 import logging