zephyr/README: Update for the current featureset, add more info.

zephyr/README.md

@@ -6,12 +6,20 @@ This is an initial port of MicroPython to Zephyr RTOS
 
 The port integrates well with Zephyr build system, using the latest
 features which will be available in 1.6.0, and thus requires Zephyr
-master to build against. All boards supported by Zephyr should be
-supported (but not all were tested).
+master to build against. All boards supported by Zephyr (with standard
+level of feature support, like UART console) should work with
+MicroPython (but not all were tested).
 
-At this time, only basic interactive prompt (REPL) over UART connection
-is supported. Over time, bindings for various Zephyr subsystems may
-be added.
+Features supported at this time:
+
+* REPL (interactive prompt) over Zephyr UART console.
+* `utime` module for time measurements and delays.
+* `machine.Pin` class for GPIO control.
+* "Frozen modules" support to allow to bundle Python modules together
+  with firmware. Including complete applications, including with
+  run-on-boot capability.
+
+Over time, bindings for various Zephyr subsystems may be added.
 
 
 Building
@@ -36,10 +44,33 @@ supported boards.
 Running
 -------
 
-To run the resulting application in QEMU (for BOARDs like qemu_x86,
+To run the resulting firmware in QEMU (for BOARDs like qemu_x86,
 qemu_cortex_m3):
 
     make qemu
 
-For deploying/flashing the application on a real board, follow Zephyr
+For deploying/flashing a firmware on a real board, follow Zephyr
 documentation for a given board.
+
+
+Quick example
+-------------
+
+To blink an LED:
+
+    import time
+    from machine import Pin
+
+    LED = Pin(("GPIO_1", 21), Pin.OUT)
+    while True:
+        LED.value(1)
+        time.sleep(0.5)
+        LED.value(0)
+        time.sleep(0.5)
+
+The above code uses an LED location for a FRDM-K64F board (port B, pin 21;
+following Zephyr conventions port are identified by "GPIO_x", where *x*
+starts from 0). You will need to adjust it for another board (using board's
+reference materials). To execute the above sample, copy it to clipboard, in
+MicroPython REPL enter "paste mode" using Ctrl+E, paste clipboard, press
+Ctrl+D to finish paste mode and start execution.