[docs] add contributing guide

CONTRIBUTING.rst

@@ -0,0 +1,95 @@
+Contributing
+============
+
+Installing Dependencies
+-----------------------
+
+Make sure you are running Python 2.7::
+
+  $ python -V
+  Python 2.7.x
+
+Install:
+
+1. `Pip <https://pip.pypa.io/en/stable/installing/>`_
+2. `Terraform <https://www.terraform.io/intro/getting-started/install.html>`_
+
+Fork the StreamAlert repository from the UI, and then clone it locally::
+
+  $ git clone https://github.com/<your-username>/streamalert.git
+
+Change into the cloned StreamAlert repo, and install Python dependencies::
+  
+  $ cd streamalert
+  $ pip install -r requirements.txt
+
+Making Changes
+--------------
+
+Checkout a new branch::
+  
+  git checkout -b <branch-name>
+
+Make changes, add features, or fix bugs.
+
+When writing commit messages, make sure to prefix with one of the following tags::
+
+  [docs]              # changes to StreamAlert documentation
+  [cli]               # stream_alert_cli changes
+  [lambda][alert]     # stream_alert lambda changes
+  [lambda][output]    # stream_alert_output lambda changes
+  [terraform]         # terraform changes
+  [core]              # changes with core stream_alert classes used across both functions
+  [testing]           # changes with testing infrastructure or processes
+  [setup]             # StreamAlert development setup changes
+
+The first line of your commit message should be short.  Use newlines to explain further::
+
+  [tag] short description
+
+  * longer explanation of what the change is
+  * with added context
+
+.. note:: Please squash your similar commits into one.
+
+Tests
+-----
+
+Unit Testing
+~~~~~~~~~~~~
+
+StreamAlert contains unit tests for many parts of the code.  When making changes, you need to ensure that you do  not break existing functionality.  To run unit tests locally::
+
+  $ nosetests -v test/unit
+
+Each test should end with ``... ok``, and finally you should see ``OK`` at the end.
+
+If you are making changes which require test refactoring, please do so.
+
+If you are adding features to existing classes with tests, you must add test cases to verify your changes.
+
+Integration Testing
+~~~~~~~~~~~~~~~~~~~
+
+To verify StreamAlert end to end locally, follow the testing instructions `here <https://streamalert.io/rules.html>`_. 
+
+Pull Request
+------------
+
+Once your branch is ready, push it to your forked repository, and make a pull-request to the main ``airbnb/streamalert`` repo.
+
+The title of your pull request should be a short description of your changes.
+
+In your pull request body, use the following template::
+
+  to @airbnb/streamalert-maintainers
+
+  size: small|medium|large
+  resolves: #1              # only add this if there's a relevant open issue related to this PR
+
+  * summary of changes 1
+  * summary of changes 2
+  
+All pull requests must pass continuous integration tests (nosetests) and receive a code review from one of the maintainers.
+
+After your branch has been accepted, you are free to merge into ``master``!