If environment variable SPEC_OPTS is present, it will override any
cli options passed to rspec.  This may cause problems, particular in
regards to UI notifications.  This commit adds a UI warning to alert
users to this potential problem.

The underlying issue is that if SPEC_OPTS defines it's own formatter,
the custom formatter will not be used and that formatter is what
generates notifications.
update readme to include note about possible SPEC_OPTS conflict
Merge pull request #156 from phallstrom/warn_about_env_spec_opts

Warn about env SPEC_OPTS causing notification problems.