Fixed a spelling mistake.

doc/html/index.html

@@ -441,7 +441,7 @@ When you start a kernel image with 1, you are telling it to start in runlevel
 
 <p>
 
-Why on the subject, it should be pointed at the setting up init and its 
+While on the subject, it should be pointed at the setting up init and its 
 runlevels is one of the
 most challenging areas of creating a bootable root_fs.&nbsp;&nbsp;Often 
 your creation will only work with "single" until all the conflicts