Add some internal docs links for Args/ArgsOs

[jtdowney]

In many places the docs link to other sections and I noticed it was lacking here. Not sure if there is a standard for if inter-linking is appropriate.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @sfackler (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

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[steveklabnik]

@bors: r+ rollup

thank you!

Not sure if there is a standard for if inter-linking is appropriate.

Nope, just areas we haven't gotten to yet. Adding more links would be wonderful, feel free to send in as many of these PRs as you'd like 😄

[bors]

📌 Commit 9170ddf has been approved by steveklabnik