Buck Documentation - Additional details for `deps_query` argument
Buck Documentation - Additional details for `deps_query` argument

Summary:
Wasted time trying to figure out `deps_query` when querying a different target. Didn't realize you had to have the other target included in deps for the query to work.

Updated docs accordingly.

Reviewed By: cjhopman

fbshipit-source-id: 35d04ea68897be7b475f0443cbf78fb9d6578c30

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