Fix and improve texts in ypbind(8) #1886133
    
    Fix typos & basic grammar and try to re-phrase some sentences in
    sections added to ypbind(8).
    
    List of changes:
    
     *  Fixed typos.
    
     *  Fixed grammar errors.
    
     *  Fixed '45s' spelling.
    
     *  Simplified part about wait timeout.
    
     *  Re-phrased the intro to avoid mentioning "In Fedora"; this really
        is about systemd (which is also used on rhel7/8 and more Fedora
        derivatives.)
    
     *  Simplified part about DHCP and PEERNIS.