fetch doc: update note on '+' in front of the refspec
fetch doc: update note on '+' in front of the refspec

While it is not *wrong* per-se to say that pulling a rewound/rebased
branch will lead to an unnecessary merge conflict, that is not what
the leading "+" sign to allow non-fast-forward update of remote-tracking
branch is at all.

Helped-by: Marc Branchaud <e9ae0fa8a6ea1c4a34faf6d3356cfe5d659ec9d4@xiplink.com>
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