Cosmetic: Fix a number of typos, no functional changes.

Fix various misspellings of things like "environment", "kernel",
"default" and "volatile", and throw in a couple grammar fixes.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
diff --git a/board/RPXlite_dw/README b/board/RPXlite_dw/README
index 14296b2..9e2d0f4 100644
--- a/board/RPXlite_dw/README
+++ b/board/RPXlite_dw/README
@@ -87,9 +87,9 @@
 
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-A word on the U-Boot enviroment variable setting and usage :
+A word on the U-Boot environment variable setting and usage :
 
-In the beginning, you could just need very simple defult environment variable setting,
+In the beginning, you could just need very simple default environment variable setting,
 like[include/configs/RPXlite.h] :
 
 #define CONFIG_BOOTCOMMAND                                                      \