README: Add simple build instructions

Add a list of commands to build.

Signed-off-by: Yasushi SHOJI <[email protected]>

Author: yashi

README.md

@@ -1 +1,14 @@
 # Tests for libcsp on Zephyr RTOS
+
+## How to build
+
+```
+mkdir workspace
+cd workspace
+pipenv shell
+pip3 install west
+west init -m https://github.com/spacecubics/libcsp-zephyr
+west update
+pip3 install -r zephyr/scripts/requirements-base.txt
+west build -b qemu_cortex_m3 libcsp-zephyr
+```