docs: clarify "preserve" option wording for git-pull

The "also" sounds as if "preserve" does a rebase as an additional
step that "true" would not do, but that is not the case.  Clarify
this by omitting "also", and rewording the sentence a bit.

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-pull.txt

@@ -111,9 +111,8 @@ include::merge-options.txt[]
 	was rebased since last fetched, the rebase uses that information
 	to avoid rebasing non-local changes.
 +
-When preserve, also rebase the current branch on top of the upstream
-branch, but pass `--preserve-merges` along to `git rebase` so that
-locally created merge commits will not be flattened.
+When set to preserve, rebase with the `--preserve-merges` option passed
+to `git rebase` so that locally created merge commits will not be flattened.
 +
 When false, merge the current branch into the upstream branch.
 +