Add contribution information

Author: gmr

CONTRIBUTING.md

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+# Contributing
+
+## Test Coverage
+
+To contribute to Consulate, please make sure that any new features or changes
+to existing functionality **include test coverage**.
+
+*Pull requests that add or change code without coverage have a much lower chance
+of being accepted.*
+
+## Prerequisites
+
+Consulate test suite has a couple of requirements:
+
+ * Dependencies from [requirements/testing.txt](requirements/testing.txt) are installed
+ * Local Docker and [docker-compose](https://docs.docker.com/compose/)
+
+## Installing Dependencies
+
+You may want to develop in a virtual environment. This is usually done inside the source
+repository, and `.gitignore` is configured to ignore a virtual environment in `env`.
+
+```bash
+python3 -m venv env
+source env/bin/activate
+```
+
+To install the dependencies needed to run Consulate tests, use
+
+```bash
+pip install -r requirements/testing.txt
+```    
+
+## Starting the test dependency
+
+Prior to running tests, ensure that Consul is running via Docker using:
+
+```bash
+./bootstrap
+```
+    
+This script uses [docker-compose](https://docs.docker.com/compose/) to launch a Consul server container that is
+pre-configured for the tests. In addition, it configures `build/test-environment` that is loaded
+by the tests with configuration information for connecting to Consul.
+
+## Running Tests
+
+To run all test suites, run:
+
+    nosetests
+
+## Code Formatting
+
+Please format your code using [yapf](http://pypi.python.org/pypi/yapf)
+with ``pep8`` style prior to issuing your pull request. In addition, run
+``flake8`` to look for any style errors prior to submitting your PR.
+
+Both are included when the test requirements are installed. If you are fixing
+formatting for existing code, please separate code-reformatting commits from 
+functionality changes.