MLBEDSW-2054 Add README.md
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+# Ethos-u Core Driver
+
+This repository contains a device driver for the Ethos-u NPU.
+
+## Building
+
+The source code comes with a CMake based build system. The driver is expeced
+to be cross compiled for any of the supported Arm Cortex-m CPUs, which will
+require the user to setup a custom toolchain file.
+
+The user is also required to define `CMAKE_SYSTEM_PROCESSOR` for the target CPU,
+for example cortex-m55+nodsp+nofp. This can be done either in the toolchain
+file or on the command line.
+
+```
+$ mkdir build
+$ cd build
+$ cmake .. -DCMAKE_TOOLCHAIN_FILE=<toolchain> -DCMAKE_SYSTEM_PROCESSOR=cortex-m<nr><features>
+$ make
+```