README: Remove sporadic tabs

Indentation was already done mainly with spaces, so this commit
removes the tabs and makes some of the whitespace more consistent.

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