It's okay for v8.

How can I add in Odoo 11? 

somebody please tell me where should i write the code. I am using odoo 8.0 in localhost on my system.

You see here: https://www.odoo.com/documentation/8.0/reference/reports.html

The reports belong to a model will gather into the print submenu of that model

Example:

<report
    id="account_invoices_1"
    model="account.invoice"
    string="Invoices 1"
    report_type="qweb-pdf"
    name="account.report_invoice_1"
    file="account.report_invoice_1"
    attachment_use="True"
    attachment="(object.state in ('open','paid')) and
        ('INV'+(object.number or '').replace('/','')+'.pdf')"
/>

<report
    id="account_invoices_2"
    model="account.invoice"
    string="Invoices_2"
    report_type="qweb-pdf"
    name="account.report_invoice_2"
    file="account.report_invoice_2"
    attachment_use="True"
    attachment="(object.state in ('open','paid')) and
        ('INV'+(object.number or '').replace('/','')+'.pdf')"
/>     

<report

id = "invoice_report_temp"

string = "Proforma Invoice"

model = "account.invoice"

report_type = "QWEB-pdf"

name = "modulename.template name"

file = "module name.templatename"

/>