chore: update README with a note on development of v4

README.md

@@ -12,17 +12,7 @@ SPDX-License-Identifier: MPL-2.0
 [![Downloads](https://static.pepy.tech/badge/openstef/month)](https://pepy.tech/project/openstef)
 [![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/5585/badge)](https://bestpractices.coreinfrastructure.org/projects/5585)
 
-<!-- SonarCloud badges -->
-
-[![Bugs](https://sonarcloud.io/api/project_badges/measure?project=OpenSTEF_openstef&metric=bugs)](https://sonarcloud.io/dashboard?id=OpenSTEF_openstef)
-[![Code Smells](https://sonarcloud.io/api/project_badges/measure?project=OpenSTEF_openstef&metric=code_smells)](https://sonarcloud.io/dashboard?id=OpenSTEF_openstef)
-[![Coverage](https://sonarcloud.io/api/project_badges/measure?project=OpenSTEF_openstef&metric=coverage)](https://sonarcloud.io/dashboard?id=OpenSTEF_openstef)
-[![Duplicated Lines (%)](https://sonarcloud.io/api/project_badges/measure?project=OpenSTEF_openstef&metric=duplicated_lines_density)](https://sonarcloud.io/dashboard?id=OpenSTEF_openstef)
-[![Maintainability Rating](https://sonarcloud.io/api/project_badges/measure?project=OpenSTEF_openstef&metric=sqale_rating)](https://sonarcloud.io/dashboard?id=OpenSTEF_openstef)
-[![Reliability Rating](https://sonarcloud.io/api/project_badges/measure?project=OpenSTEF_openstef&metric=reliability_rating)](https://sonarcloud.io/dashboard?id=OpenSTEF_openstef)
-[![Security Rating](https://sonarcloud.io/api/project_badges/measure?project=OpenSTEF_openstef&metric=security_rating)](https://sonarcloud.io/dashboard?id=OpenSTEF_openstef)
-[![Technical Debt](https://sonarcloud.io/api/project_badges/measure?project=OpenSTEF_openstef&metric=sqale_index)](https://sonarcloud.io/dashboard?id=OpenSTEF_openstef)
-[![Vulnerabilities](https://sonarcloud.io/api/project_badges/measure?project=OpenSTEF_openstef&metric=vulnerabilities)](https://sonarcloud.io/dashboard?id=OpenSTEF_openstef)
+> **Note:** OpenSTEF v4 is actively under development in the [`release/v4.0.0`](https://github.com/OpenSTEF/openstef/tree/release/v4.0.0) feature branch. Pre-releases are already available on [PyPI](https://pypi.org/project/openstef/#history), give them a try and share your feedback!
 
 OpenSTEF is a Python package designed for generating short-term forecasts in the energy sector. The repository includes all the essential components required for machine learning pipelines that facilitate the forecasting process. To utilize the package, users are required to furnish their own data storage and retrieval interface.
 
@@ -32,11 +22,16 @@ OpenSTEF is a Python package designed for generating short-term forecasts in the
 - [Table of contents](#table-of-contents)
 - [External information sources](#external-information-sources)
 - [Installation](#installation)
+  - [Install the openstef package](#install-the-openstef-package)
+    - [Remark regarding installation within a **conda environment on Windows**](#remark-regarding-installation-within-a-conda-environment-on-windows)
+  - [Remark regarding installation on Apple Silicon](#remark-regarding-installation-on-apple-silicon)
+    - [Remark regarding installation with minimal XGBoost dependency](#remark-regarding-installation-with-minimal-xgboost-dependency)
 - [Usage](#usage)
   - [Example notebooks](#example-notebooks)
   - [Reference Implementation](#reference-implementation)
-  - [Database connector for OpenSTEF](#database-connector-for-openstef)
-- [License](license)
+  - [Database connector for openstef](#database-connector-for-openstef)
+- [License](#license)
+  - [Licenses third-party libraries](#licenses-third-party-libraries)
 - [Contributing](#contributing)
 - [Contact](#contact)