docs: Add conda-forge install instructions (sbi-dev#1340)

* Add install instructions from conda-forge for pixi and conda to README.
   - c.f. https://github.com/conda-forge/sbi-feedstock
* Add conda-forge badge.
* Add install instructions from conda-forge for pixi and conda to docs.
   - Correct minimum required Python to Python 3.9.
   - Update example python version in conda env creation to Python 3.12.

README.md

@@ -1,4 +1,5 @@
 [![PyPI version](https://badge.fury.io/py/sbi.svg)](https://badge.fury.io/py/sbi)
+[![Conda Version](https://img.shields.io/conda/vn/conda-forge/sbi.svg)](https://github.com/conda-forge/sbi-feedstock)
 [![Contributions welcome](https://img.shields.io/badge/contributions-welcome-brightgreen.svg?style=flat)](https://github.com/sbi-dev/sbi/blob/master/CONTRIBUTING.md)
 [![Tests](https://github.com/sbi-dev/sbi/actions/workflows/ci.yml/badge.svg)](https://github.com/sbi-dev/sbi/actions)
 [![codecov](https://codecov.io/gh/sbi-dev/sbi/branch/main/graph/badge.svg)](https://codecov.io/gh/sbi-dev/sbi)
@@ -62,22 +63,36 @@ posterior = inference.build_posterior()
 performance in some cases. We recommend using a virtual environment with
 [`conda`](https://docs.conda.io/en/latest/miniconda.html) for an easy setup.
 
-To install `sbi`, follow these steps:
+If `conda` is installed on the system, an environment for installing `sbi` can be created as follows:
 
-1. **Create a Conda Environment** (if using Conda):
+```
+conda create -n sbi_env python=3.9 && conda activate sbi_env
+```
+
+### From PyPI
+
+To install `sbi` from PyPI run
+
+```
+python -m pip install sbi
+```
 
-   ```bash
-   conda create -n sbi_env python=3.9 && conda activate sbi_env
-   ```
+### From conda-forge
 
-2. **Install `sbi`**: Independent of whether you are using `conda` or not, `sbi` can be
-   installed using `pip`:
+To install and add `sbi` to a project with [`pixi`](https://pixi.sh/), from the project directory run
+
+```
+pixi add sbi
+```
+
+and to install into a particular conda environment with [`conda`](https://docs.conda.io/projects/conda/), in the activated environment run
+
+```
+conda install --channel conda-forge sbi
+```
 
-  ```commandline
-  pip install sbi
-  ```
+### Test the installation
 
-3. **Test the installation**:
 Open a Python prompt and run
 
 ```python

docs/docs/index.md

@@ -39,7 +39,7 @@ samples = posterior.sample((1000,), x=x_o)
 **To get started, install the `sbi` package with:**
 
 ```commandline
-pip install sbi
+python -m pip install sbi
 ```
 
 for more advanced install options, see our [Install Guide](install.md).

docs/docs/install.md

@@ -1,23 +1,35 @@
 # Installation
 
-`sbi` requires Python 3.8 or higher. A GPU is not required, but can lead to
+`sbi` requires Python 3.9 or higher. A GPU is not required, but can lead to
 speed-up in some cases. We recommend using a
 [`conda`](https://docs.conda.io/en/latest/miniconda.html) virtual environment
 ([Miniconda installation
 instructions](https://docs.conda.io/en/latest/miniconda.html)). If `conda` is
 installed on the system, an environment for installing `sbi` can be created as
 follows:
 
-```commandline
+```console
 # Create an environment for sbi (indicate Python 3.8 or higher); activate it
-$ conda create -n sbi_env python=3.10 && conda activate sbi_env
+$ conda create -n sbi_env python=3.12 && conda activate sbi_env
 ```
 
 Independent of whether you are using `conda` or not, `sbi` can be installed
 using `pip`:
 
-```commandline
-pip install sbi
+```
+python -m pip install sbi
+```
+
+To install and add `sbi` to a project with [`pixi`](https://pixi.sh/), from the project directory run
+
+```
+pixi add sbi
+```
+
+and to install into a particular conda environment with [`conda`](https://docs.conda.io/projects/conda/), in the activated environment run
+
+```
+conda install --channel conda-forge sbi
 ```
 
 To test the installation, drop into a Python prompt and run