stm32: Suggest putting code in main.py not boot.py.

Don't want users to accidentally use boot.py (because recovering requires
knowing how to activate safe mode).

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

docs/pyboard/tutorial/usb_mouse.rst

@@ -8,8 +8,8 @@ To do this we must first edit the ``boot.py`` file to change the USB
 configuration.  If you have not yet touched your ``boot.py`` file then it
 will look something like this::
 
-    # boot.py -- run on boot-up
-    # can run arbitrary Python, but best to keep it minimal
+    # boot.py -- run on boot to configure USB and filesystem
+    # Put app code in main.py
 
     import pyb
     #pyb.main('main.py') # main script to run after this one

ports/cc3200/mptask.c

@@ -99,8 +99,8 @@ OsiTaskHandle svTaskHandle;
 static fs_user_mount_t *sflash_vfs_fat;
 
 static const char fresh_main_py[] = "# main.py -- put your code here!\r\n";
-static const char fresh_boot_py[] = "# boot.py -- run on boot-up\r\n"
-    "# can run arbitrary Python, but best to keep it minimal\r\n"
+static const char fresh_boot_py[] = "# boot.py -- run on boot to configure USB and filesystem\r\n"
+    "# Put app code in main.py\r\n"
                                     #if MICROPY_STDIO_UART
     "import os, machine\r\n"
     "os.dupterm(machine.UART(0, " MP_STRINGIFY(MICROPY_STDIO_UART_BAUD) "))\r\n"

ports/stm32/factoryreset.c

@@ -37,8 +37,8 @@
 #if MICROPY_VFS_FAT
 
 static const char fresh_boot_py[] =
-    "# boot.py -- run on boot-up\r\n"
-    "# can run arbitrary Python, but best to keep it minimal\r\n"
+    "# boot.py -- run on boot to configure USB and filesystem\r\n"
+    "# Put app code in main.py\r\n"
     "\r\n"
     "import machine\r\n"
     "import pyb\r\n"