Updated the README to describe the build commands with Maven.
The previous commands were a remnant when the plugin still used gradle.
Testing done
Tried the commands in this PR. → They work.
### Submitter checklist
- [x] Make sure you are opening from a **topic/feature/bugfix branch** (right side) and not your main branch!
- [x] Ensure that the pull request title represents the desired changelog entry
- [x] Please describe what you did
- [x] Link to relevant issues in GitHub or Jira → NA
- [x] Link to relevant pull requests, esp. upstream and downstream changes
- [x] Ensure you have provided tests - that demonstrates feature works or fixes the issue
Updated the README to describe the build commands with Maven. The previous commands were a remnant when the plugin still used gradle.
Testing done
Tried the commands in this PR. → They work.