hello_world: add beautiful README

Apps/hello_world/README.md

@@ -1,3 +1,15 @@
-This target is a basic test to check if the RTOS and UART is working correctly.
+# What is this thing?
 
-Connect a UART to PA10 (TX) and PA9 (RX) using a FTDI like FT232H at a baudrate of 4MBaud.
+This application (hello_world) sets up the clock tree, UART and FreeRTOS to verify its functionality
+
+# How?
+
+Connect a UART (FT232 or whatever) to PA10 (TX) and PA9 (RX).
+
+# And now?
+
+Open picocom on your FT232 at 4MBaud:
+
+`# picocom -b 4000000 /dev/ttyUSB0` 
+
+And you will see a piece of text every second spit out by a FreeRTOS task.