Added file "SOURCECODEINTRO"

SOURCECODEINTRO.md

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+# Introduction to the Source Code
+
+## .github
+
+#### issue_template.md
+Contains a template for reporting issues you may
+discover while using the app
+
+#### pull_request_template.md
+Contains a template for requirements that must be met before submitting
+a pull request
+
+## app
+
+### libs
+
+#### aspose-cells-19.3-android.via.java.jar
+[Aggregated](https://docs.oracle.com/javase/8/docs/technotes/guides/jar/jarGuide.html) library
+
+### src
+
+#### androidTest/test
+Contain unit and application tests
+
+#### main
+Contains main java files for application
+
+### Other files:
+
+#### build.gradle
+Gradle build script
+
+#### proguard-rules.pro
+[Proguard](https://guides.codepath.com/android/Configuring-ProGuard) specifications
+
+## config
+
+#### checkstyle.gradle / checkstyle_config.xml
+[Gradle Checkstyle plugin](https://docs.gradle.org/current/userguide/checkstyle_plugin.html), for quality checks
+
+## gradle
+[Gradle](https://docs.gradle.org/current/userguide/getting_started_eng.html) is our build tool  
+This folder contains the [Gradle wrapper](https://docs.gradle.org/current/userguide/gradle_wrapper_basics.html) files, 
+
+## screenshots
+Contains images of the app in use
+
+## Other Files:
+
+#### .gitignore
+Specifies which files should be [ignored](https://git-scm.com/docs/gitignore) by Git
+
+#### .travis.yml / _config.yml
+Config files
+
+#### CONTRIBUTING.md
+Instructions for contributing to the project
+
+#### LICENSE.md
+Contains our [license](https://gist.github.com/kn9ts/cbe95340d29fc1aaeaa5dd5c059d2e60)
+
+#### README.md
+Introduction to the project, walkthrough of usage, list of dependencies
+
+#### build.gradle
+Gradle build script
+
+#### gradle.properties
+Project-wide [Gradle](https://docs.gradle.org/current/userguide/getting_started_eng.html) settings
+
+#### gradlew / gradlew.bat
+Contain the [Gradle wrapper](https://docs.gradle.org/current/userguide/gradle_wrapper_basics.html) script
+
+#### settings.gradle
+Contains the [Gradle](https://docs.gradle.org/current/userguide/gradle_basics.html) settings file to define a root project name and subprojects
+