docs: add code of conduct (#339)

Since we are working on governance I figured it would be a good time to
add a
code of conduct. To start with I aimed for the relevant bits from ASF
and
Wikimedia. I highly encourage others to contribute here and help add
things
they feel we should cover.

---------

Co-authored-by: Jeroen van Straten <jeroen.van.straten@gmail.com>
Co-authored-by: David Sisson <EpsilonPrime@users.noreply.github.com>

CODE_OF_CONDUCT.md

@@ -0,0 +1,81 @@
+# Code of Conduct
+
+We believe in creating a diverse, inclusive, and accessible environment for
+contributors in order to create the best software.  To achieve this we expect
+everyone who participates in the project to observe the following guidelines.
+
+## Guidelines
+
+These guidelines are not exhaustive or complete.
+
+### Be open
+
+We invite anyone to participate in our community.  We prefer to use public methods of communication only.  We are patient in discussion and know that
+people come from various time zones and may not be able to respond immediately.
+We know that significant decisions should not occur on fast-paced
+communication channels like Slack.
+
+We do not hide our intentions.  We have many reasons to work on this project
+and many of us are paid for our work and will profit from the success of the
+project.  We are transparent with our goals and our reasoning.
+
+We are honest and we promptly admit to our mistakes while being understanding that others may also make mistakes.
+
+### Be respectful
+
+We show respect for others in all of our communications.  We practice empathy
+and we always try to understand what the other person is telling us.  We are
+willing to challenge our own understanding and adapt it when needed.
+
+We always assume good faith unless there is clear evidence to the contrary.
+We assume that others working on this project have the same goal in mind and
+that their intentions are genuine.
+
+We respect the way that contributors name and describe themselves.  When
+others express a preference for particular names or pronouns then we are
+mindful of this fact and use these words when communicating with or about
+the person.
+
+### Be collaborative
+
+We understand that this project is created for everyone and not just ourselves.
+We explain our work to others and encourage others to expand on our work.  We
+recognize that decisions we make will affect others and we take those
+consequences seriously when making these decisions.
+
+We help newcomers integrate into the project, mentor them, and point them
+towards appropriate resources.  We do our best to learn answers before we ask questions.  We recognize and credit the work done by contributors.  We thank
+others for their hard work and give credit where it is due.
+
+## Unacceptable Behavior
+
+The following specific behaviors are unacceptable and will not be tolerated.
+
+* Insults: This includes name calling, using slurs or stereotypes, and any attacks based on personal characteristics
+* Sexual harassment: Sexual attention or advances of any kind towards others where the person knows or reasonably should know that the attention is unwelcome or in situations where consent cannot be communicated.
+* Sexist, racist, or otherwise discriminatory jokes and language.
+* Posting sexually explicit or violent material.
+* Posting (or threatening to post) other people's personally identifying information ("doxing") or private content.
+* Excessive or unnecessary profanity.
+* Repeated harassment of others. In general, if someone asks you to stop, then stop.
+* Trolling: Deliberately disrupting conversations or posting in bad-faith to intentionally provoke.
+* Advocating for, or encouraging, any of the above behaviour.
+
+## Reporting Guidelines
+
+We all work together to help others identify and call out instances where
+our code of conduct is not being observed.  We remember to assume good faith
+and recognize that contributors may be having a bad day or may not be aware
+their behavior violates the code of conduct.  Often, calling attention to
+negative behavior is sufficient to resolve the issue.
+
+When a situation becomes difficult to resolve or we feel that the conversation
+is getting out of control we can email the SMC at substrait-harassment@googlegroups.com.
+
+## Acknowledgements
+
+This statement draws on the following for content and inspiration:
+
+ * [The Apache Software Foundation code of conduct](https://www.apache.org/foundation/policies/conduct.html)
+ * [Wikimedia's Universal Code of Conduct](https://meta.wikimedia.org/wiki/Universal_Code_of_Conduct)
+