feature #9393 Added concrete example document (Michelle Sanver, michellesanver)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes #9393).

Discussion
----------

Added concrete example document

In a meeting that took place the 21st of February 2018 we defined this list as a start to a concrete example document, to specifically list out some things that are unwanted behaviour.

Commits
-------

cccf869 Update concrete_example_document.rst
c762418 Syntax
201738f Updated to say that some jokes are not ok
7911a86 Added concrete example document

Author: fabpot

contributing/code_of_conduct/concrete_example_document.rst

@@ -0,0 +1,30 @@
+Code of Conduct: Concrete Example Document
+==========================================
+
+This is a living document that serves to give concrete examples of
+unwanted behaviour. These examples have all taken place somewhere in the
+PHP community in the past, and are clear code of conduct violations
+according to the Symfony code of conduct.
+
+Concrete Examples
+-----------------
+
+* Unwelcome comments regarding a person’s lifestyle choices and practices,
+  including those related to food, health, parenting, drugs, and employment;
+* Deliberate misgendering or use of `dead names`_ (The birth name
+  of a person who has since changed their name, often a transgender person);
+* Threats of violence like "The person that created this PR should be
+  punched in the face";
+* Incitement of violence towards any individual, including encouraging a
+  person to commit suicide or to engage in self-harm (even as a joke);
+* Sustained disruption of discussion;
+* Pattern of inappropriate social contact, such as requesting/assuming
+  inappropriate levels of intimacy with others;
+* Continued one-on-one communication after requests to cease;
+* Putting down people based on their technology choices or their work.
+
+The original list is inspired and modified from `geek feminism`_ and
+confirmed by experiences from PHPWomen.
+
+.. _dead names: https://en.wiktionary.org/wiki/deadname
+.. _geek feminism: https://geekfeminism.org/about/code-of-conduct