Bashhub installation can break without notifying users.

A handful of installs have broken due to changes in a users shell environment or changes in configuration (e.g. lack of auth token, or bad config file). This causes commands to not save properly without letting the user know at all.

It'd be nice to do some basic checks on session start to verify that Bashhub is working. If not, we can output a helpful warning message to notify a user that their installation needs to be fixed. #27 (closed) is one example that's popped up in the past few months.