documentation/update readme to fix array reference

[rm0nroe]

First, thank you for referencing this repository from twitter-scraper #197

In setup, I found that you have a typo in your readme. It errors in that "tweets" is not found. See below:

all_tweets = app.get_tweets()
for tweet in tweets:

for tweet in tweets: should be updated to for tweet in all_tweets:

Cheers 🍻

[mahrtayyab]

Thank you so much , it is fixed now.