Updated Docs

[metju90]

Documented that if retry_stategy is provided, errors are not emitted

[metju90]

I've spent half a day trying to figure out why errors are not being emitted. Only to find the following comment in node_modules/redis/index.js:

 // Only emit the error if the retry_stategy option is not set
    if (!this.options.retry_strategy) {
        this.emit('error', err);
    }