Doc: Update python_installation.rst (AMICI-dev#2212)

* Update python_installation.rst

On Python 3.11 and with openblas 0.3.24-2, amici installer is unable to find "cblas.h". This is fixed by exporting the openblas path to BLAS_CFLAGS

* Apply suggestions from code review

* Update python_installation.rst

exporting BLAS_LIBS  was also needed to get the amici package to be importable, in addition to BLAS_CFLAGS

---------

Co-authored-by: Daniel Weindl <dweindl@users.noreply.github.com>

documentation/python_installation.rst

@@ -79,6 +79,13 @@ Install the AMICI dependencies via ``pacman``
 
    sudo pacman -S python swig openblas gcc hdf5 boost-libs
 
+Export the bash variables ``BLAS_CFLAGS`` and ``BLAS_LIBS`` to point to where BLAS was installed, e.g.:
+
+.. code-block:: bash
+
+  export BLAS_CFLAGS="-I/usr/include/openblas/"
+  export BLAS_LIBS="-lopenblas"
+
 Install AMICI:
 
 .. code-block:: bash
@@ -99,7 +106,14 @@ Alternatively:
 
    sudo pacman -Su python swig openblas gcc hdf5 boost-libs
 
-3. Install AMICI:
+3. Export the bash variables ``BLAS_CFLAGS`` and ``BLAS_LIBS`` to point to where BLAS was installed, e.g.:
+
+.. code-block:: bash
+
+  export BLAS_CFLAGS="-I/usr/include/openblas/"
+  export BLAS_LIBS="-lopenblas"
+
+4. Install AMICI:
 
 .. code-block:: bash