Give Subreddit Stats user the option to enter a subreddit name if he didn't include it in the arguments

#### Changes
* As described in title.
* Prints out the name of the subreddit user is going to analyze. This is helpful since I've been in situations where the script is in the middle of analyzing submissions when I realize I've chosen the wrong subreddit to analyze.

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Feel free to change whatever is necessary, and give feedback on the quality of this pull request.