Documentation/kernel-parameters.txt: add min_addr, fix max_addr

Add "min_addr" documentation.
For "max_addr", add nn before [KMG] since a number is needed and this
is consistent with other uses of [KMG].

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>