Inconsistency in Java version between Prerequisites and Docker build instructions

Hello! While reviewing the documentation to set up the project, I noticed a discrepancy regarding the required Java version:

- In the Prerequisites section, it is stated that Java 17 is required to build and run alf.io.
- However, in the Generate Docker image section, the experimental Docker command uses a Gradle image based on JDK 11:
docker run --rm ... gradle:7.0.0-jdk11 gradle ...

Running a build with JDK 11 when the project is configured for Java 17 may lead to compilation errors (e.g., class file version mismatch) or unexpected behavior in the generated distribution.

Suggested Fix:
Update the Docker command in the README to use a JDK 17 compatible image, for example:
docker run --rm -u gradle -v "$PWD":/home/gradle/project -w /home/gradle/project gradle:7.4-jdk17 gradle --no-daemon distribution -x test