add_users_to_cache: Add new users to the cache
In alexpghayes/twittercache: Sample the Twitter Graph and Cache It Locally

Notes:

1	add_users_to_cache(users, edges)

users

The calling function is responsible for making sure that the user isn't already in the cache
If user A and user B are friends, and we add both user A and user B, we will duplicate any edges between A and B.
Doesn't record information about protected accounts, treats these as failed queries.
We only take the first 5,000 friends and 5,000 followers for the time being. The idea is that for important edges, the edge will get picked up from the other node. This may miss out on edges between node both with huge follower and following counts, but who cares about those.