docs: pr: use origin remote name instead of upstream
    
    In 99% of cases, the remote it called 'origin'. It seems silly to have a
    differently named remote in example docs, especially when it contains a
    hint to copy over a particular line into git config files, that requires
    the users to change the line over and over for each time they use it.
    
    Also improve formatting and some whitespace.
    
    Signed-off-by: Kamil Páral <kparal@redhat.com>
    
    Merges https://pagure.io/pagure/pull-request/2950