Add readme file

README.md

+# Concordant client library
+
+[![License](https://img.shields.io/badge/license-MIT-green)](https://opensource.org/licenses/MIT)
+
+Concordant client library in Kotlin for the Concordant platform API.
+
+## Requirements
+
+- Download and install Gradle from [Gradle website](https://gradle.org/install/);
+
+## Project overview
+
+The code of the version v0 is in the directory *src/*.
+
+The pseudo code of the version v1 is in the directory *pseudo-code-v1/*.
+
+## Build project
+
+The building is managed through the use of Gradle.
+
+*gradle build*: compiles code.