Added CONTRIBUTING. [ci skip]

CONTRIBUTING.md

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+# Contributing to alexa-app
+
+You're encouraged to submit [pull requests](https://github.com/alexa-js/alexa-app/pulls), [propose features and discuss issues](https://github.com/alexa-js/alexa-app/issues).
+
+In the examples below, substitute your Github username for `contributor` in URLs.
+
+### Fork the Project
+
+Fork the [project on Github](https://github.com/alexa-js/alexa-app) and check out your copy.
+
+```
+git clone https://github.com/contributor/alexa-app.git
+cd alexa-app
+git remote add upstream https://github.com/alexa-js/alexa-app.git
+```
+
+### Run Tests
+
+Ensure that you can build the project and run tests.
+
+```
+npm install
+npm test
+```
+
+## Contribute Code
+
+### Create a Topic Branch
+
+Make sure your fork is up-to-date and create a topic branch for your feature or bug fix.
+
+```
+git checkout master
+git pull upstream master
+git checkout -b my-feature-branch
+```
+
+### Write Tests
+
+Try to write a test that reproduces the problem you're trying to fix or describes a feature that you want to build. Tests live under [test](test).
+
+We definitely appreciate pull requests that highlight or reproduce a problem, even without a fix.
+
+### Write Code
+
+Implement your feature or bug fix.
+
+Make sure that `npm test` completes without errors.
+
+### Write Documentation
+
+Document any external behavior in the [README](README.md).
+
+### Commit Changes
+
+Make sure git knows your name and email address:
+
+```
+git config --global user.name "Your Name"
+git config --global user.email "contributor@example.com"
+```
+
+Writing good commit logs is important. A commit log should describe what changed and why.
+
+```
+git add ...
+git commit
+```
+
+### Push
+
+```
+git push origin my-feature-branch
+```
+
+### Make a Pull Request
+
+Go to https://github.com/alexa-js/alexa-app and select your feature branch. Click the 'Pull Request' button and fill out the form. Pull requests are usually reviewed within a few days.
+
+Add more commits or amend your previous commit with any changes.
+
+```
+git commit --amend
+git push origin my-feature-branch -f
+```
+
+### Rebase
+
+If you've been working on a change for a while, rebase with upstream/master.
+
+```
+git fetch upstream
+git rebase upstream/master
+git push origin my-feature-branch -f
+```
+
+### Check on Your Pull Request
+
+Go back to your pull request after a few minutes and see whether it passed muster with Travis-CI. Everything should look green, otherwise fix issues and amend your commit as described above.
+
+### Be Patient
+
+It's likely that your change will not be merged and that the nitpicky maintainers will ask you to do more, or fix seemingly benign problems. Hang on there!
+
+## Thank You
+
+Please do know that we really appreciate and value your time and work. We love you, really.