Adding r/harrypotter to the list of subreddits bot

[Beneficial-Insurance]

Adds r/harrypotter to the list of subreddits to which the bot responds. I mean, there are a suprising number of fanfiction threads in the threads.

[tusing]

Thanks for the PR. This subreddit is intentionally left out because the large userbase and traffic flow will overload the bot despite the stream-based approach it currently takes.