Documentation: Write some docu

* Safety notice
* HW modifications
* Links to PCB repo

doc/source/hardware/frontend.rst

@@ -8,5 +8,3 @@ Schematic
 
 .. image:: frontend-schematic_v1.2.svg
    :target: /_images/frontend-schematic_v1.2.svg
-
-

doc/source/hardware/index.rst

@@ -10,3 +10,11 @@ This guide on the reflow controller's hardware is based on the ``reflow-oven-con
 	:glob:
 
 	*
+
+Links
+-----
+
+- `Reflow Oven Control PCB v1.2 schematic <https://git.shimatta.de/attachments/788fde4e-a560-445b-87ea-de1d67f6846a>`__
+- `Git Repository for Controller PCB <https://git.shimatta.de/pcb/reflow-oven-control-pcb>`__
+
+

doc/source/hardware/modifications.rst

@@ -0,0 +1,15 @@
+.. _hardware_modifications:
+
+Hardware Modifications
+======================
+
+Analog Frontend
+---------------
+
+.. note::
+	Solder a ``100 nF`` capacitor parallel to ``R315`` in order to implement a low pass characteristic of the difference amplifier in the :ref:`analog frontend<hw_analog_fe>`. This massively increases EMI performance which prevents the :ref:`ADC Watchdog<firmware_meas_adc_watchdog>` from triggering.
+
+Power Supply
+------------
+.. note::
+	Replace transformer ``BV-EI-303-2010`` with ``BV-EI-303-2050``, which has the same footprint but a little more power and does not heat that much.