docs/renesas-ra: Add renesas-ra docs files.

Signed-off-by: Takeo Takahashi <takeo.takahashi.xv@renesas.com>

docs/renesas-ra/tutorial/program_in_flash.rst

@@ -0,0 +1,62 @@
+.. _renesas-ra_program_in_flash:
+
+Write a program in internal file system
+=======================================
+
+Internal file system
+--------------------
+
+The FAT file system is created and initialized in the RA MCU's internal
+flash when the MicroPython starts at the first time on the board.
+The file system is mounted as "/flash", so you can access this flash system
+and create a program file into the /flash directory.
+
+As the factory setting, following size is allocated for the file system:
+
+===============  ===================
+    Board         File System Size
+---------------  -------------------
+ EK-RA4M1           36KB ( 36864B)
+ EK-RA4W1           64KB ( 65536B)
+ EK-RA6M1          128KB (131072B)
+ EK-RA6M2          256KB (262144B)
+ RA4M1 CLICKER      36KB ( 36864B)
+===============  ===================
+
+As the factory setting, following 2 files are created in the file system:
+
+* boot.py : executed first when the system starts
+* main.py : executed after boot.py completes
+
+Write a program in the internal file system
+-------------------------------------------
+
+You can write a program in main.py which is executed automatically
+when the MicroPython starts. For example, you can write LED blinking
+program like below::
+
+    import os
+    os.getcwd()
+    f = open('main.py', 'rw+')
+    print(f.read())
+    f.write('import time\n')
+    f.write('from machine import Pin\n')
+    f.write('led1 = Pin(Pin.cpu.P106)\n')
+    f.write('while True:\n')
+    f.write('    led1.on()\n')
+    f.write('    time.sleep(1)\n')
+    f.write('    led1.off()\n')
+    f.write('    time.sleep(1)\n')
+    f.close()
+    f = open('main.py', 'r')
+    print(f.read())
+    f.close()
+
+Entering CTRL-D for software reset, the MicroPython reboots, displays
+following messages::
+
+    MPY: sync filesystems
+    MPY: soft reboot
+
+and main.py is executed and LED1 blinks per 1 second.
+If you want to stop the program, please enter CTRL-C.