The text is copied from the io module docs and looks correct. I am not familiar with the proper formatting in .c files, in particular, the initial blank line. I changed the titles and news items because 'add documentation' usually means 'add to the .rst doc file'.

Looks okay to me.

If you are worried about the Arg Clinic formatting Terry, I would compare it to the surrounding functions (e.g. readlines directly above), or the existing io.BytesIO.writelines Clinic code, and check the resulting __doc__ attributes.

Hi @vadmium, @terryjreedy,
Seems a blank line is required due to: https://mail.python.org/pipermail/python-dev/2013-June/127110.html
Lack of a blank line causes a clinic error: https://github.com/python/cpython/blob/master/Tools/clinic/clinic.py#L4808

Same docstring should be added to Lib/_pyio.py

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@methane Thanks for the suggestion, I just added requested docs to _pyio

Anyway, I'm really sorry for notification to all reviewers. Accidentally I made a merge in my branch and a lot of reviewers were added to this PR. I'm really Sorry guys.

Thanks @n0npax for the PR, and @methane for merging it 🌮🎉.. I'm working now to backport this PR to: 3.7.
🐍🍒⛏🤖

Sorry, @n0npax and @methane, I could not cleanly backport this to 3.7 due to a conflict.
Please backport using cherry_picker on command line.
cherry_picker ab86521a9d9999731e39bd9056420bb7774fd144 3.7

GH-12905 is a backport of this pull request to the 3.7 branch.