Removed unnecessary installation instructions (#256)

README.md

@@ -28,22 +28,15 @@ Enjoying scikit-gmsh? Show your support with a [GitHub star](https://github.com/
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 - [Installation](#installation)
-  - [Pip](#pip)
 - [Usage](#usage)
 - [License](#license)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
 
 ## Installation
 
-scikit-gmsh is available on [PyPI](https://pypi.org/project/scikit-gmsh/).
-
-### Pip
-
 [![pypi](https://img.shields.io/pypi/v/scikit-gmsh?style=for-the-badge&label=pypi&logo=python&logoColor=white)](https://pypi.org/project/scikit-gmsh/)
 
-scikit-gmsh is also available on [PyPI](https://pypi.org/project/scikit-gmsh/):
-
 ```shell
 pip install scikit-gmsh
 ```