Documentation issue: actions.write with args content

Documentation URL: https://docs.bazel.build/versions/master/skylark/lib/actions.html#write

"May be a either a string or an actions.args() object." is all it says about passing an args object to `content` here. What does that actually *do* though? How are the args processed? What is the intended use case?

Start with the actions.write section at the linked actions.html#write documentation page, then investigate how an actions.args() object is processed when passed as content. Update the documentation to explain that processing and the intended use case, including enough detail for users to understand when to pass an args object.

Written by the indexing model from the issue text.