adding visual examples of package features on index page

* the sphinx gallery examples are used to visualize the different
  features of the library that link to the getting started page

---------

Co-authored-by: Philip Loche <[email protected]>

Author: agoscinski

docs/src/getting-started.rst

@@ -8,6 +8,8 @@ our :ref:`installation` instructions for installing ``scikit-matter``.
 For a detailed explaination of the functionalities, please look at the
 :ref:`selection-api`
 
+.. _getting_started-selection:
+
 Features and Samples Selection
 ------------------------------
 
@@ -21,6 +23,8 @@ Notebook Examples
    :start-line: 4
 
 
+.. _getting_started-reconstruction:
+
 Reconstruction Measures
 -----------------------
 
@@ -33,6 +37,8 @@ Notebook Examples
 .. include:: examples/reconstruction/index.rst
    :start-line: 4
 
+.. _getting_started-pcovr:
+
 Principal Covariates Regression
 -------------------------------
 

docs/src/index.rst

@@ -1,5 +1,75 @@
 .. automodule:: skmatter
 
+.. raw:: html
+
+    <div class="container">
+        <div class="row">
+            <div class="col-sm d-flex">
+                <div class="card text-center mb-4" style="background-color: transparent">
+                <div class="card-body">
+                    <h5 class="card-title" style="margin-top: 0px">
+
+
+.. only:: html
+
+  :ref:`getting_started-selection`
+
+  .. image:: /examples/selection/images/thumb/sphx_glr_FeatureSelection-WHODataset_thumb.png
+    :alt:
+
+.. raw:: html
+
+                    </h5>
+                    <p class="card-text">Supervised and unsupervised selection
+                    methods based on
+                    CUR matrix decomposition and Farthest Point Sampling.</p>
+                </div>
+                </div>
+            </div>
+            <div class="col-sm d-flex">
+                <div class="card text-center mb-4" style="background-color: transparent">
+                <div class="card-body">
+                    <h5 class="card-title" style="margin-top: 0px">
+
+.. only:: html
+
+  :ref:`getting_started-pcovr`
+
+  .. image:: /examples/pcovr/images/thumb/sphx_glr_PCovR_thumb.png
+    :alt:
+
+.. raw:: html
+
+                    </h5>
+                    <p class="card-text">Utilises a combination between a PCA-like and a LR-like loss
+                    to determine the decomposition matrix to project feature into latent space</p>
+                </div>
+                </div>
+            </div>
+            <div class="col-sm d-flex">
+                <div class="card text-center mb-4" style="background-color: transparent">
+                <div class="card-body">
+                    <h5 class="card-title" style="margin-top: 0px">
+
+.. only:: html
+
+  :ref:`getting_started-reconstruction`
+
+  .. image:: /examples/reconstruction/images/thumb/sphx_glr_PlotLFRE_thumb.png
+    :alt:
+
+.. raw:: html
+
+                    </h5>
+                    <p class="card-text">Error measures for quantifying the
+                    linear decodable information capacity between features</p>
+                </div>
+                </div>
+            </div>
+        </div>
+    </div>
+    <br>
+
 .. include:: ../../README.rst
    :start-after: marker-issues
    :end-before: marker-contributing