Update README about no contributions (#5240)

* Update README about no contributions

README.md

@@ -1,28 +1,30 @@
+# **_Important:_** **_This project is no longer accepting contributions. We appreciate all the past contributions and support from the community._**
+
 [![Maintainability](https://api.codeclimate.com/v1/badges/0e6a23344616e29b4ed0/maintainability)](https://codeclimate.com/github/SAP/jenkins-library/maintainability)
 [![Test Coverage](https://api.codeclimate.com/v1/badges/0e6a23344616e29b4ed0/test_coverage)](https://codeclimate.com/github/SAP/jenkins-library/test_coverage)
 [![Go Report Card](https://goreportcard.com/badge/github.com/SAP/jenkins-library)](https://goreportcard.com/report/github.com/SAP/jenkins-library)
 [![REUSE status](https://api.reuse.software/badge/github.com/SAP/jenkins-library)](https://api.reuse.software/info/github.com/SAP/jenkins-library)
 
-# Project Piper Repository
+## Project Piper Repository
 
 The Project "Piper" offers default pipelines to easily implement CI/CD processes integrating SAP systems. The corresponding "Shared Library" provides a set of "steps" to build your own scenarios beyond defaults.
 
-# User Documentation
+## User Documentation
 
 If you want to view the User Documentation of Project Piper please follow this [Piper Pages Link][piper-library-user-doc].
 
-# Known Issues
+## Known Issues
 
 A list of known issues is available on the [GitHub issues page of this project][piper-library-issues].
 
-# How to obtain support
+## How to obtain support
 
 Feel free to open new issues for feature requests, bugs or general feedback on
 the [GitHub issues page of this project][piper-library-issues].
 
 Register to our [google group][google-group] in order to get updates or for asking questions.
 
-# Contributing
+## Contributing
 
 Read and understand our [contribution guidelines][piper-library-contribution]
 before opening a pull request.