A few more grammar and typo fixes from the User's Guide.

More cleanup from some of the later chapters from the User's Guide,
no functional changes.

Change-Id: Ib2860fc2574503e8107935d79db45fa96014fe3a
Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Reviewed-on: http://openocd.zylin.com/1863


Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>