[doc] Simplify installation instructions

doc/install.rst

@@ -4,27 +4,37 @@
  Installation
 ==============
 
-We support two installation modes, through pip_, or mamba_ (conda).
+We support two installation modes, through pip_, or mamba_ (conda), for two
+types of releases, stable, or beta (a.k.a. development, latest).  Choose a
+combination from the tabbed pane below.
 
-.. tab:: pip
+
+.. tab:: pip/stable
+
+   .. code-block:: sh
+
+      pip install exposed
+
+
+.. tab:: pip/beta
 
    .. code-block:: sh
 
-      # stable, from PyPI:
-      $ pip install exposed
+      pip install git+https://gitlab.idiap.ch/bob/exposed
 
-      # latest beta, directly from GitLab
-      $ pip install git+https://gitlab.idiap.ch/bob/exposed
 
-.. tab:: conda
+.. tab:: conda/stable
 
    .. code-block:: sh
 
-      # stable:
-      $ mamba install -c https://www.idiap.ch/software/bob/conda -c conda-forge exposed
+      mamba install -c https://www.idiap.ch/software/bob/conda -c conda-forge exposed
+
+
+.. tab:: conda/beta
+
+   .. code-block:: sh
 
-      # latest beta:
-      $ mamba install -c https://www.idiap.ch/software/bob/conda/label/beta -c exposed
+      mamba install -c https://www.idiap.ch/software/bob/conda/label/beta -c conda-forge exposed
 
 
 .. include:: links.rst