Do not instruct users to publish assets from other packages

[freekmurze]

This PR changes the readme so it instructs users to only publish assets by this package.
More info: https://murze.be/2016/04/publishing-package-assets-right-way/

[maknz]

We've had countless problems with the --provider option. We used to use that on the main maknz/slack repo but we got complaints of it not working. I could reproduce this locally too (maknz/slack#53).

vendor:publish seems to work all the time which is good, but it's got the downside mentioned above. One suggestion was to tag the config so at least you wouldn't get views and shit getting published from other packages, just the config.

Additionally, are you sure the proxy service provider will work? This user tried it and it didn't work, but the Laravel 5 one directly seemed to work: #1. That of course doesn't help the fact that --provider didn't work at all when I tested a fresh Laravel 5.2 install locally.

Overall I'd like to use --provider but the behaviour is so erratic.

[freekmurze]

This is the first time I've heard of this problem.

Your code does look ok to me.

Try opening an issue at the Laravel framework repo or post this problem at Laraslack to get some help.