Hardware-Mapping.md

+When designing a new board we need to specify somewhere which are all the used GPIO. This is useful in order to setup a hierarchy of namespaces and to give meaningful names to the needed GPIOs.  
+For example, assuming we are developing a new board for our rocket we will have a set of sensors, such as IMUs and barometers. These sensors will use some communication protocols, such as SPI or I2C, or maybe both.  
+In the `hwmapping.h` file we can list all the GPIOs that we need.
+  
+The `hwmapping.h` file can be found under: `skyward-boardcore/libs/miosix-kernel/arch/<your-arch>/<your-board>/interfaces_impl/`.
+
+### Example
+This example shows a simple hardware mapping file:
+- `myspi`: this namespace is used to define the GPIOs related to an SPI bus, which are `sck`, `miso` and `mosi`.
+- `mysensor`: it is a sensor that works via the SPI protocol, in fact in this namespace it is defined a chip select GPIO (`cs`). Moreover it defines another GPIO in order to receive interrupts from the sensor.
+
+```cpp
+#include "interfaces/gpio.h"
+
+namespace miosix {
+
+    namespace interfaces {
+
+        namespace myspi {
+            using sck   = Gpio<GPIOA_BASE, 5>;
+            using miso  = Gpio<GPIOA_BASE, 6>;
+            using mosi  = Gpio<GPIOA_BASE, 7>;
+        } //namespace myspi
+
+    } //namespace interfaces
+
+    namespace sensors {
+
+        namespace mysensor {
+            using cs     = Gpio<GPIOE_BASE, 7>;
+            using int1   = Gpio<GPIOC_BASE, 13>;
+        }
+
+    } //namespace sensors
+
+} //namespace miosix
+```
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