clean up 1.5.4 release notes
clean up 1.5.4 release notes

Mostly typo and small grammatical fixes with one or two rewordings for
clarity.  But note the important fix for status.relativepaths.

Signed-off-by: Jeff King <696e3fbcf235d40b6ea1ebd61c87cbea79d444e7@peff.net>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git