Add PEPs Contributing Guideline, CoC, and PR template (#712)

- Suggest posting to python-ideas first
- Commit and PR title should include PEP number

Closes https://github.com/python/peps/issues/706

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,9 @@
+<!--
+
+Please include the PEP number in the pull request title, example:
+
+```
+PEP NNN: Summary of the changes made
+```
+
+-->

CODE_OF_CONDUCT.rst

@@ -0,0 +1,13 @@
+Code of Conduct
+===============
+
+Please note that all interactions on
+`Python Software Foundation <https://www.python.org/psf-landing/>`__-supported
+infrastructure is `covered
+<https://www.python.org/psf/records/board/minutes/2014-01-06/#management-of-the-psfs-web-properties>`__
+by the `PSF Code of Conduct <https://www.python.org/psf/codeofconduct/>`__,
+which includes all infrastructure used in the development of Python itself
+(e.g. mailing lists, issue trackers, GitHub, etc.).
+
+In general this means everyone is expected to be open, considerate, and
+respectful of others no matter what their position is within the project.

CONTRIBUTING.rst

@@ -0,0 +1,29 @@
+Contributing Guidelines
+=======================
+
+To learn more about the purpose of PEPs and how to go about writing a PEP, please
+start reading at PEP 1 (`pep-0001.txt <./pep-0001.txt>`_ in this repo). Note that
+PEP 0, the index PEP, is now automatically generated, and not committed to the repo.
+
+Before writing a new PEP
+------------------------
+
+Start with a discussion in `python-ideas <https://mail.python.org/mailman/listinfo/python-ideas>`_
+mailing list to determine if the idea is PEP-able. More details about it in
+`PEP 1 <https://www.python.org/dev/peps/pep-0001/#start-with-an-idea-for-python>`_.
+
+
+Commit messages
+---------------
+
+When committing to a PEP, please always include the PEP number in the subject
+title. For example, ``PEP NNN: <summary of changes>``.
+
+
+Code of Conduct
+---------------
+
+All interactions for this project are covered by the
+`PSF Code of Conduct <https://www.python.org/psf/codeofconduct/>`_. Everyone is
+expected to be open, considerate, and respectful of others no matter their
+position within the project.

README.rst

@@ -11,6 +11,12 @@ PEPs and how to go about writing a PEP, please start reading at PEP 1
 now automatically generated, and not committed to the repo.
 
 
+Contributing to PEPs
+====================
+
+See the `Contributing Guidelines <./CONTRIBUTING.rst>`_.
+
+
 reStructuredText for PEPs
 =========================