[no ci] docs: clarify installation instructions for v2 (#387)

Author: vpratz

README.md

@@ -63,12 +63,16 @@ More tutorials are always welcome! Please consider making a pull request if you
 
 ## Install
 
-BayesFlow is available to install via pip:
+BayesFlow v2 is not yet installable via PyPI, but you can use the following command to install the latest version of the `main` branch:
 
 ```bash
-pip install bayesflow
+pip install git+https://github.com/bayesflow-org/bayesflow.git
 ```
 
+If you encounter problems with this or require more control, please refer to the instructions to install from source below.
+
+Note: `pip install bayesflow` will install the v1 version of BayesFlow.
+
 ### Backend
 
 To use BayesFlow, you will also need to install one of the following machine learning backends.

docsrc/source/index.md

@@ -64,9 +64,7 @@ More tutorials are always welcome! Please consider making a pull request if you
 
     .. tab-item:: pip
 
-        .. code-block:: bash
-
-            pip install bayesflow
+        The v2 version is not available on PyPI yet, please install from source.
 
     .. tab-item:: source