Reword a sentence bringing confusion about docker links

As [discovered][1] doing user support, the sentence `You've learned that a link creates a source container that can provide information about itself to a recipient container` is confusing.

I suggest instead `You've learned that a link allows a source container to provide information about itself to a recipient container`.

[1]: http://stackoverflow.com/questions/26652877/how-to-avoid-redundant-container-linking-in-docker-when-propagating-ip-addresses/26654203?noredirect=1#comment41945048_26654203