update README of testcontainers

testcontainers/README.md

-# #HOWTO: Write Spring Boot integration tests with a 'real' database
\ No newline at end of file
+# Codebase for the blog post [#HOWTO: Write Spring Boot integration tests with a 'real' database](https://rieckpil.de/howto-write-spring-boot-integration-tests-with-a-real-database/)
+
+Steps to run this project:
+
+1. Clone this Git repository
+2. Navigate to the folder `testcontainers`
+3. Start your Docker engine
+4. Run the tests with `mvn test`