doc/developer.texi: Add a code of conduct

See: [FFmpeg-devel] [Vote] Code of Conduct
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

doc/developer.texi

@@ -403,6 +403,35 @@ finding a new maintainer and also don't forget to update the @file{MAINTAINERS}
 
 We think our rules are not too hard. If you have comments, contact us.
 
+@section Code of conduct
+
+Be friendly and respectful towards others and third parties.
+Treat others the way you yourself want to be treated.
+
+Be considerate. Not everyone shares the same viewpoint and priorities as you do.
+Different opinions and interpretations help the project.
+Looking at issues from a different perspective assists development.
+
+Do not assume malice for things that can be attributed to incompetence. Even if
+it is malice, it's rarely good to start with that as initial assumption.
+
+Stay friendly even if someone acts contrarily. Everyone has a bad day
+once in a while.
+If you yourself have a bad day or are angry then try to take a break and reply
+once you are calm and without anger if you have to.
+
+Try to help other team members and cooperate if you can.
+
+The goal of software development is to create technical excellence, not for any
+individual to be better and "win" against the others. Large software projects
+are only possible and successful through teamwork.
+
+If someone struggles do not put them down. Give them a helping hand
+instead and point them in the right direction.
+
+Finally, keep in mind the immortal words of Bill and Ted,
+"Be excellent to each other."
+
 @anchor{Submitting patches}
 @section Submitting patches