xc7: Add README for counter_test

Signed-off-by: Filip Kokosinski <fkokosinski@antmicro.com>

xc7/counter_test/README.rst

@@ -0,0 +1,35 @@
+Counter test
+~~~~~~~~~~~~
+
+This example design features a simple 4-bit counter driving LEDs. To build the
+counter example, depending on your hardware, run:
+
+.. code-block:: bash
+   :name: example-counter-a35t-group
+
+   TARGET="arty_35" make -C counter_test
+
+
+.. code-block:: bash
+   :name: example-counter-a100t-group
+
+   TARGET="arty_100" make -C counter_test
+
+
+.. code-block:: bash
+   :name: example-counter-basys3-group
+
+   TARGET="basys3" make -C counter_test
+
+Now you can upload the design with:
+
+.. code-block:: bash
+
+   openocd -f ${INSTALL_DIR}/conda/share/openocd/scripts/board/digilent_arty.cfg -c "init; pld load 0 top.bit; exit"
+
+
+The result should be as follows:
+
+.. image:: ../../docs/images/counter-example-arty.gif
+   :align: center
+   :width: 50%