Add "Contributor Covenant".

* CODE-OF-CONDUCT: New file, adapted from
  <http://contributor-covenant.org/version/1/3/0/code_of_conduct.txt>.
* doc/contributing.texi (Contributing): Mention it.
* Makefile.am (EXTRA_DIST): Add it.

CODE-OF-CONDUCT

@@ -0,0 +1,48 @@
+Contributor Code of Conduct
+
+As contributors and maintainers of this project, and in the interest of
+fostering an open and welcoming community, we pledge to respect all
+people who contribute through reporting issues, posting feature
+requests, updating documentation, submitting pull requests or patches,
+and other activities.
+
+We are committed to making participation in this project a
+harassment-free experience for everyone, regardless of level of
+experience, gender, gender identity and expression, sexual orientation,
+disability, personal appearance, body size, race, ethnicity, age,
+religion, or nationality.
+
+Examples of unacceptable behavior by participants include:
+
+* The use of sexualized language or imagery
+* Personal attacks
+* Trolling or insulting/derogatory comments
+* Public or private harassment
+* Publishing other's private information, such as physical or electronic
+addresses, without explicit permission
+* Other unethical or unprofessional conduct
+
+Project maintainers have the right and responsibility to remove, edit,
+or reject comments, commits, code, wiki edits, issues, and other
+contributions that are not aligned to this Code of Conduct, or to ban
+temporarily or permanently any contributor for other behaviors that they
+deem inappropriate, threatening, offensive, or harmful.
+
+By adopting this Code of Conduct, project maintainers commit themselves
+to fairly and consistently applying these principles to every aspect of
+managing this project. Project maintainers who do not follow or enforce
+the Code of Conduct may be permanently removed from the project team.
+
+This Code of Conduct applies both within project spaces and in public
+spaces when an individual is representing the project or its community.
+
+Instances of abusive, harassing, or otherwise unacceptable behavior may
+be reported by contacting a project maintainer at guix-maintainers@gnu.org.
+All complaints will be reviewed and investigated and will
+result in a response that is deemed necessary and appropriate to the
+circumstances. Maintainers are obligated to maintain confidentiality
+with regard to the reporter of an incident.
+
+This Code of Conduct is adapted from the Contributor Covenant
+(http://contributor-covenant.org), version 1.3.0, available at
+http://contributor-covenant.org/version/1/3/0/

Makefile.am

@@ -299,6 +299,7 @@ EXTRA_DIST =						\
   HACKING						\
   ROADMAP						\
   TODO							\
+  CODE-OF-CONDUCT					\
   .dir-locals.el					\
   build-aux/build-self.scm				\
   build-aux/hydra/gnu-system.scm			\

doc/contributing.texi

@@ -7,6 +7,15 @@ grow!  Please get in touch with us on @email{guix-devel@@gnu.org} and
 reports, patches, and anything that may be helpful to the project.  We
 particularly welcome help on packaging (@pxref{Packaging Guidelines}).
 
+@cindex code of conduct, of contributors
+@cindex contributor covenant
+In the interest of welcoming everyone who thinks this is a great project
+to contribute to---which it is, indeed!---contributors express their
+commitment to providing a warm, friendly, and harassment-free experience
+by agreeing to our ``Contributor Covenant'', adapted from
+@url{http://contributor-covenant.org/}, and which can be found in the
+@file{CODE-OF-CONDUCT} file in the source tree.
+
 @menu
 * Building from Git::           The latest and greatest.
 * Running Guix Before It Is Installed::  Hacker tricks.