Add contribution guidelines

CONTRIBUTING.md

@@ -0,0 +1,58 @@
+# How to contribute
+
+We like to encourage you to contribute to the repository.  This should be as
+easy as possible for you but there are a few things to consider when
+contributing.  The following guidelines for contribution should be followed if
+you want to submit a pull request.
+
+## How to prepare
+
+* You need a [GitHub account](https://github.com/signup/free)
+* Submit an [issue ticket](https://github.com/otris/vscode-janus-debug/issues) for your
+  issue if there isn't one yet.
+  * Describe the issue and include steps to reproduce if it's a bug.
+  * Ensure to mention the earliest version that you know is affected.
+* If you are able and want to fix this, fork the repository on GitHub.
+
+## Make Changes
+
+* In your forked repository, create a topic branch for your upcoming patch.
+  (e.g. `feature-autodiscover` or `bugfix-windows-crash`)
+  * Usually this is based on the master branch.
+  * Create a branch based on master; `git branch
+  my-work master` then checkout the new branch with `git
+  checkout my-work`.  Please avoid working directly on the `master` branch.
+* Make sure you stick to the existing coding style.
+* Prior to committing, stage your changes and run `git clang-format` if it is
+  available on your platform.
+* Make commits of logical units and describe them properly. See
+  [How to Write a Git Commit Message](http://chris.beams.io/posts/git-commit/).
+* Check for unnecessary white space with `git diff --check` before committing.
+* If possible, submit tests to your patch / new feature so it can be tested easily.
+* Assure nothing is broken by running all the tests, if possible.
+* You should use `git pull --rebase` instead of `git pull` to avoid generating
+  a non-linear history in your clone. To configure `git pull` to pass
+  `--rebase` by default on the master branch, run the following command:
+
+ ```
+ git config branch.master.rebase true
+ ```
+
+## Submit Changes
+
+* Push your changes to a topic branch in your fork of the repository.
+* Open a pull request to the original repository and choose the right original
+  branch you want to patch.
+* If not done in commit messages (which you really should do) please reference
+  and update your issue with the code changes. But _please do not close the
+  issue yourself_.
+* Even if you have write access to the repository, do not directly push or
+  merge pull-requests. Let another team member review your pull request and
+  approve.
+
+# Additional Resources
+
+* [General GitHub documentation](http://help.github.com/)
+* [GitHub pull request documentation](http://help.github.com/send-pull-requests/)
+* [Read the Issue Guidelines by @necolas](https://github.com/necolas/issue-guidelines/blob/master/CONTRIBUTING.md) for more details
+