docs: add warning that LMM does not work on frozen macOS app (#55)

docs/sec_getting_started.rst

@@ -2,6 +2,8 @@
 Getting started
 ===============
 
+.. _sec_installation:
+
 Installation
 ============
 Shape-Out 2 can be installed via multiple channels.
@@ -19,9 +21,9 @@ Shape-Out 2 can be installed via multiple channels.
 
    .. code:: bash
 
-       pip install shapeout2
+       python3 -m pip install shapeout2
 
-   To start Shape-Out, simply run ``python -m shapeout2``
+   To start Shape-Out, simply run ``python3 -m shapeout2``
    or ``shapeout2`` in a command shell. 
 
 

docs/sec_qg_lme4.rst

@@ -8,6 +8,13 @@ significance (p-value) when comparing two measurement groups. The analysis
 uses linear mixed effects models (LMM) as described in :cite:`Herbig2018`
 and yields results identical to those obtained with Shape-Out 1.
 
+.. warning::
+    Unfortunately, LMM analysis currently does not work with the .app or
+    .pkg bundle on macOS. This problem is tracked in `issue #73
+    <https://github.com/ZELLMECHANIK-DRESDEN/ShapeOut2/issues/73>`_.
+    If you are using macOS and you would like to use LMM analysis, you have to
+    install Shape-Out 2 as a Python package (see :ref:`sec_installation`).
+
 The LMM analysis is performed using the lme4 R package
 and is based on the :ref:`implementation in dclab <dclab:sec_av_lme4>`
 (please read for more information on the options available) which uses