Create contributing.md

CONTRIBUTING.md

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+Checklist (and a short version for the impatient)
+=================================================
+
+  * Commits:
+
+    - Make commits of logical units.
+
+    - Check for unnecessary whitespace with "git diff --check" before
+      committing.
+
+    - Commit using Unix line endings (check the settings around "crlf" in
+      git-config(1)).
+
+    - Do not check in commented out code or unneeded files.
+
+    - The first line of the commit message should be a short
+      description (50 characters is the soft limit, excluding ticket
+      number(s)), and should skip the full stop.
+
+    - Associate the issue in the message. The first line should include
+      the issue number in the form "(GH-#XXXX) Rest of message".
+
+    - The body should provide a meaningful commit message, which:
+
+      - uses the imperative, present tense: "change", not "changed" or
+        "changes".
+
+      - includes motivation for the change, and contrasts its
+        implementation with the previous behavior.
+
+    - Make sure that you have tests for the bug you are fixing, or
+      feature you are adding.
+
+    - Make sure the test suites passes after your commit:
+      `bundle exec rspec spec/acceptance` More information on [testing](#Testing) below
+
+    - When introducing a new feature, make sure it is properly
+      documented in the README.md
+
+  * Submission:
+
+    * Pre-requisites:
+
+      - Make sure you have a [GitHub account](https://github.com/join)
+
+    * Preferred method:
+
+      - Fork the repository on GitHub.
+
+      - Push your changes to a topic branch in your fork of the
+        repository. (the format GH-1234-short_description_of_change is
+        usually preferred for this project).
+
+      - Submit a pull request to the repository.