Update crashkernel-howto.txt
    
    upstream: fedora
    related:  bz2003832
    conflict: none
    
    commit 7435ecf3c43c0d15dc103c964043facce4b21a37
    Author: Kairui Song <kasong@redhat.com>
    Date:   Wed Jul 21 14:05:25 2021 +0800
    
        Update crashkernel-howto.txt
    
        Fix some grammar issues.
    
        Signed-off-by: Kairui Song <kasong@redhat.com>
    
    Signed-off-by: Tao Liu <ltao@redhat.com>