Merge pull request #405 from ajnavarro/contributing

Add CONTRIBUTING.md file.

Author: ajnavarro

CONTRIBUTING.md

@@ -0,0 +1,57 @@
+# source{d} Contributing Guidelines
+
+source{d} projects accept contributions via GitHub pull requests.
+This document outlines some of the
+conventions on development workflow, commit message formatting, contact points,
+and other resources to make it easier to get your contribution accepted.
+
+## Certificate of Origin
+
+By contributing to this project you agree to the [Developer Certificate of
+Origin (DCO)](DCO). This document was created by the Linux Kernel community and is a
+simple statement that you, as a contributor, have the legal right to make the
+contribution.
+
+In order to show your agreement with the DCO you should include at the end of commit message,
+the following line: `Signed-off-by: John Doe <john.doe@example.com>`, using your real name.
+
+This can be done easily using the [`-s`](https://github.com/git/git/blob/b2c150d3aa82f6583b9aadfecc5f8fa1c74aca09/Documentation/git-commit.txt#L154-L161) flag on the `git commit`.
+
+## Support Channels
+
+The official support channels, for both users and contributors, are:
+
+- GitHub issues: each repository has its own list of issues.
+- Slack: join the [source{d} Slack](https://join.slack.com/t/sourced-community/shared_invite/enQtMjc4Njk5MzEyNzM2LTFjNzY4NjEwZGEwMzRiNTM4MzRlMzQ4MmIzZjkwZmZlM2NjODUxZmJjNDI1OTcxNDAyMmZlNmFjODZlNTg0YWM) community.
+
+*Before opening a new issue or submitting a new pull request, it's helpful to
+search the project - it's likely that another user has already reported the
+issue you're facing, or it's a known issue that we're already aware of.
+
+## How to Contribute
+
+Pull Requests (PRs) are the main and exclusive way to contribute code to source{d} projects.
+In order for a PR to be accepted it needs to pass a list of requirements:
+
+- The contribution must be correctly explained with natural language and providing a minimum working example that reproduces it.
+- All PRs must be written idiomaticly:
+    - for Go: formatted according to [gofmt](https://golang.org/cmd/gofmt/), and without any warnings from [go lint](https://github.com/golang/lint) nor [go vet](https://golang.org/cmd/vet/)
+    - for other languages, similar constraints apply.
+- They should in general include tests, and those shall pass.
+    - If the PR is a bug fix, it has to include a new unit test that fails before the patch is merged.
+    - If the PR is a new feature, it has to come with a suite of unit tests, that tests the new functionality.
+    - In any case, all the PRs have to pass the personal evaluation of at least one of the [maintainers](MAINTAINERS).
+
+### Format of the commit message
+
+Every commit message should describe what was changed, under which context and, if applicable, the GitHub issue it relates to:
+
+```
+plumbing: packp, Skip argument validations for unknown capabilities. Fixes #623
+```
+
+The format can be described more formally as follows:
+
+```
+<package>: <subpackage>, <what changed>. [Fixes #<issue-number>]
+```