add note about timeouts and connection integrity

[shmargum]

After a long time of investigating difficult to reproduce errors and suspecting that there is some thread safety issue, we found a note at the bottom of the connection pool gem (which we don't use): https://github.com/mperham/connection_pool which indicates that Timeout::timeout may cause strange errors Then, we wrapped our redis calls in small timeouts and were quickly able to reproduce the errors