Add Maven Central badges

[jsajlovic]

Basic information

• nrich version: v1.1.0
• Module: all

Description

Summary

Added GitHub badges for Maven Central.

Details

• updated root readme file
• added Maven Central badge to each module's readme file

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Enhancement (non-breaking change which enhances existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix, enhancement or feature that would cause existing functionality to change in backward-incompatible way)
• Docs change
• Refactoring
• Dependency upgrade

Checklist

• I have read the project's CONTRIBUTING document
• I have checked my code with the project's static analysis tooling
• I have formatted my code with the project's IDEA code-style configuration
• I have checked my code for misspellings
• I have organized my changes in easy-to-follow commits
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests pass.