Add a code of conduct

After reading some discussions I would like to point several things:
- The [viadeSpec](https://arquisoft.github.io/viadeSpec/) is a _living document_ as you can see in the title, so you must look at it as a working draft or proposal rather than as a real specification. The goal is to have a channel to discuss about a common data model for routes representation that can help interoperability.
- The proposal is not mandatory and the different teams can decide if they accept or not parts or the whole data model. My suggestion is that you take a look at [Postel's law](https://en.wikipedia.org/wiki/Robustness_principle) when you implement your systems.
- The spec should not be affected by time considerations of the different teams, i.e. is a change is good to improve the specification, then it could be accepted even if that change can affect the implementations. The goal is to provide a good-enough spec for a route management system
- Please, try to be polite when you propose or discuss the issues and respect other people's opinions. My advice is that you focus your comments only on the technical aspects of your proposal leaving out any comment about your laboratory assignment, your team work, personal preferences, etc.

The previous notes could be part of a code of conduct file that we can add to the repository.

Review the notes in issue #26 and the linked viadeSpec context before choosing the repository's code-of-conduct document location. Done means adding a code of conduct file that captures the collaboration and discussion guidance described in the issue.

Written by the indexing model from the issue text.