Hi!

You can import them with a custom module and an xml data file like this (in 7 version, but this should be equivalent in 8 version):

<?xml version="1.0" encoding="UTF-8"?>
<openerp>
    <data>
        <record id="partner_1" model="res.partner">
            <field name="name">Partner 1</field>
            <field name="company_id" ref="base.main_company"/>
            <field name="parent_id" ref="base.main_company"/>
            <field name="customer" eval="False"/>
            <field name="country_id" ref="base.fr"/>
        </record>
        <record id="user_1" model="res.users">
            <field name="partner_id" ref="partner_1"/>
            <field name="login">partner1</field>
            <field name="password">o0YneDzGo</field>
            <field name="name">Partner 1</field>
            <field name="signature">Partner 1</field>
            <field name="company_id" ref="base.main_company"/>
            <field name="groups_id" eval="[(4,ref('account.group_account_user'))]"/>
            <field name="groups_id" eval="[(4,ref('account.group_account_invoice'))]"/>
        </record>
        <record id="partner_2" model="res.partner">
            <field name="name">Partner 2</field>
            <field name="company_id" ref="base.main_company"/>
            <field name="parent_id" ref="base.main_company"/>
            <field name="customer" eval="False"/>
            <field name="country_id" ref="base.fr"/>
        </record>
        <record id="user_2" model="res.users">
            <field name="partner_id" ref="partner_2"/>
            <field name="login">partner2</field>
            <field name="password">IzWJt4nu</field>
            <field name="name">Partner 2</field>
            <field name="signature">Partner 2</field>
            <field name="company_id" ref="base.main_company"/>
            <field name="groups_id" eval="[(4,ref('account.group_account_user'))]"/>
        </record>
    </data>
</openerp> 

See also: https://www.odoo.com/documentation/8.0/howtos/backend.html

Bye!

I checked the 'more' options button and there is no 'import' option there. I think you can create a separate view with a method that method has to read a CSV file into array of dictionaries, one per user, and call the res_users.create method per user, this will update your database. Some trials are needed to adjust the dictionary to not miss any field.

export their user names and passwor to a csv file, then use import utility of odoo to import them to odoo database.