Add README, LICENSE, and instructions

Author: christoomey

LICENSE.md

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+The MIT License (MIT)
+
+Copyright © 2015-2018 [thoughtbot, inc.](http://thoughtbot.com)
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the “Software”), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# Refactoring / Explaining Variable
+
+Hey there! We're [thoughtbot](https://thoughtbot.com), a design and
+development consultancy that brings your digital product ideas to life.
+We also love to share what we learn.
+
+This coding exercise comes from [Upcase](https://thoughtbot.com/upcase),
+the online learning platform we run. It's part of the
+[Refactoring](https://thoughtbot.com/upcase/refactoring) course and is just one small sample of all
+the great material available on Upcase, so be sure to visit and check out the rest.
+
+## Exercise Intro
+
+In this exercise, you'll be extracting explaining variables within the `total` method of `Tipper`.
+
+An explaining variable is a variable whose name describes the purpose of the expression you're assigning to it. It's used to help break down longer, more complex expressions, making the final expression more manageable and easier to understand.
+
+[Read more about explaining variables](http://refactoring.com/catalog/extractVariable.html).
+
+## Instructions
+
+To start, you'll want to clone and run the setup script for the repo
+
+    git clone [email protected]:thoughtbot-upcase-exercises/explaining-variable.git
+    cd explaining-variable
+    bin/setup
+
+Extract a few new variables whose names explain their purpose.
+
+Make sure the tests are passing by running:
+
+    rake
+
+## Featured Solution
+
+Check out the [featured solution branch](https://github.com/thoughtbot-upcase-exercises/explaining-variable/compare/featured-solution#toc) to
+see the approach we recommend for this exercise.
+
+## Forum Discussion
+
+If you find yourself stuck, be sure to check out the associated
+[Upcase Forum discussion](https://forum.upcase.com/t/refactoring-explaining-variable/4636)
+for this exercise to see what other folks have said.
+
+## Next Steps
+
+When you've finished the exercise, head on back to the
+[Refactoring](https://thoughtbot.com/upcase/refactoring) course to find the next exercise,
+or explore any of the other great content on
+[Upcase](https://thoughtbot.com/upcase).
+
+## License
+
+explaining-variable is Copyright © 2015-2018 thoughtbot, inc. It is free software,
+and may be redistributed under the terms specified in the
+[LICENSE](/LICENSE.md) file.
+
+## Credits
+
+![thoughtbot](https://presskit.thoughtbot.com/assets/images/logo.svg)
+
+This exercise is maintained and funded by
+[thoughtbot, inc](http://thoughtbot.com/community).
+
+The names and logos for Upcase and thoughtbot are registered trademarks of
+thoughtbot, inc.