README: `Alternately' -> `Alternatively'

Also, one `Alternate' was changed to `Alternative' for the
sake of consistency.

Signed-off-by: Michael Witten <mfwitten@gmail.com>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>