Add README.md file

README.md:
- Add file that specifies installation, configuration, build, and maintainer details for this project.

README.md

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+# Installation
+1. Clone this repository by entering this command into Bash:
+```bash
+git clone git@github.com:david-read-iii/The-Guardian-News-Client.git
+```
+2. Then, open the root project directory in Android Studio.
+
+# Configuration
+## Specify a The Guardian API key in Gradle BuildConfigs
+1. Register for your The Guardian API key from [this site](https://open-platform.theguardian.com/access/).
+2. Create a `theguardianapikey.properties` file in the root project directory.
+3. Put the following info into the file. Replace `...` with your key. Replacing `...` with `test` should be sufficient for limited testing purposes:
+```properties
+THE_GUARDIAN_API_KEY="..."
+```
+
+# Build APK or Android App Bundle
+1. From *Android Studio*, go to the *Build* menu.
+2. Go to the *Build Bundle(s) / APK(s)* menu.
+3. Select either *Build APK(s)* or *Build Bundle(s)*.
+4. Wait for a notification to pop signifying the operation completion.
+5. Select *locate* in the notification to navigate to the file location of the built artifact.
+6. Install the artifact on your Android device and try it out.
+
+# Maintainers
+This project is mantained by:
+* [David Read](http://github.com/david-read-iii)