Documentation/git-filter-branch: Move note about effect of removing commits

Documentation/git-filter-branch: Move note about effect of removing commits

The note that explains that changes introduced by removed commits are
preserved should be placed directly after the paragraph that describes
such commits removal.  Otherwise the reference to "the commits" appears
out of context.

Also the big example that follows "Consider this history" is about
rewriting part of the history DAG.  Move the paragraph that
describes the operation close to it.

Signed-off-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>