bpo-36523: Add docstring to io.IOBase.writelines

[n0npax]

Add docs to io.IOBase.writelines

https://bugs.python.org/issue36523

[terryjreedy]

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'.

[vadmium]

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.

[n0npax]

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

[methane]

Same docstring should be added to Lib/_pyio.py

[the-knights-who-say-ni]

Hello, and thanks for your contribution!

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[n0npax]

@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.

[miss-islington]

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

[miss-islington]

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

[bedevere-bot]

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