Add default values for environment variables

This should reduce errors by some values not being set in the .env file - namely 2FA and Theme

main.py

@@ -20,7 +20,7 @@ reddit_object = get_subreddit_threads()
 
 load_dotenv()
 length, number_of_comments = save_text_to_mp3(reddit_object)
-download_screenshots_of_reddit_posts(reddit_object, number_of_comments, os.getenv("THEME"))
+download_screenshots_of_reddit_posts(reddit_object, number_of_comments, os.getenv("THEME", "light"))
 download_background()
 chop_background_video(length)
 final_video = make_final_video(number_of_comments)

reddit/subreddit.py

@@ -15,7 +15,7 @@ def get_subreddit_threads():
 
     print_step("Getting AskReddit threads...")
 
-    if os.getenv("REDDIT_2FA").lower() == "yes":
+    if os.getenv("REDDIT_2FA", default="no").lower() == "yes":
         print(
             "\nEnter your two-factor authentication code from your authenticator app.\n"
         )