Doc:Install or build>Build>Unix>Run a first simulation: Update the instruction...

Doc:Install or build>Build>Unix>Run a first simulation: Update the instruction to install BornAgain Python package

hugo/content/installation/building/unix/first-simulation.md

@@ -13,13 +13,16 @@ This section explains how to run a first simulation.
 
 #### Post installation steps
 
-After the installation is complete, the location of the BornAgain libraries needs to be included into the `LD_LIBRARY_PATH` (or `DYLD_LIBRARY_PATH` for MacOS) and `PYTHONPATH` environment variables. This can be done by running the BornAgain setup script in a terminal:
-
+If a Python package is produced in the build phase, then after installation, the Python package ('wheel') can be found under the folder
+`<install_dir>/python/<python-version>/wheel`.
+The wheel can be installed via `pip`; for instance
 ```bash
-source <install_dir>/bin/thisbornagain.sh
+python3 -m pip install BornAgain-<detailed-version>.whl
+```
+or
+```bash
+pip3 install BornAgain-<detailed-version>.whl
 ```
-
-This command can also be placed in your `.bashrc` file (`.profile` for MacOS) to avoid having to run this command for each terminal session.
 
 #### Running the first Python simulation
 
@@ -41,10 +44,10 @@ Run an example and enjoy your first BornAgain simulation plot.
 ```python
 python <install_dir>/share/BornAgain-{{< release-string-short >}}/Examples/scatter2d/CylindersAndPrisms.py
 ```
- 
+
 #### Running the BornAgain GUI
 
 The BornAgain application can be run by executing following command
 ```bash
 $ <install_dir>/bin/bornagain
-```
\ No newline at end of file
+```