[ADD] accounting: add Singapore localisations

Impacted versions:

- saas-16.4 or above

This commit improve below features:

- Singapore accounting documentation
- PayNow QR code documentation

task-3130633

Part-of: odoo/documentation#4565

content/applications/finance/fiscal_localizations.rst

@@ -108,7 +108,7 @@ available on Odoo.
 - Portugal - Accounting
 - Romania - Accounting
 - Saudi Arabia - Accounting
-- Singapore - Accounting
+- :doc:`Singapore - Accounting <fiscal_localizations/singapore>`
 - Slovak - Accounting
 - Slovenian - Accounting
 - South Africa - Accounting
@@ -148,6 +148,7 @@ available on Odoo.
    fiscal_localizations/mexico
    fiscal_localizations/netherlands
    fiscal_localizations/peru
+   fiscal_localizations/singapore
    fiscal_localizations/spain
    fiscal_localizations/switzerland
    fiscal_localizations/united_arab_emirates

content/applications/finance/fiscal_localizations/singapore.rst

@@ -0,0 +1,54 @@
+=========
+Singapore
+=========
+
+Add PayNow QR codes to invoices
+===============================
+
+PayNow is a payment service platform that allows customers to make instant domestic payments to
+individuals and merchants in Singapore dollars via online and mobile banking.
+
+Activate QR codes
+-----------------
+
+Go to :menuselection:`Accounting --> Configuration --> Settings`. Under the :guilabel:`Customer
+Payments` section, activate the :guilabel:`QR Codes` feature.
+
+PayNow bank account configuration
+---------------------------------
+
+Go to :menuselection:`Contacts --> Configuration --> Bank Accounts` and select the bank account for
+which you want to activate PayNow. Set the :guilabel:`Proxy Type` and fill in the :guilabel:`Proxy
+Value` field depending on the type you chose.
+
+.. important::
+   - The account holder's country must be set to Singapore on its contact form.
+   - You could also include the invoice number in the QR code by checking the :guilabel:`Include
+     Reference` checkbox.
+
+.. image:: singapore/sg-paynow-bank-setting.png
+   :alt: PayNow bank account configuration
+
+.. seealso::
+   :doc:`../accounting/bank`
+
+Bank journal configuration
+--------------------------
+
+Go to :menuselection:`Accounting --> Configuration --> Journals`, open the bank journal, then fill
+out the :guilabel:`Account Number` and :guilabel:`Bank` under the :guilabel:`Journal Entries` tab.
+
+.. image:: singapore/sg-bank-account-journal-setting.png
+   :alt: Bank Account's journal configuration
+
+Issue invoices with PayNow QR codes
+-----------------------------------
+
+When creating a new invoice, open the :guilabel:`Other Info` tab and set the :guilabel:`Payment
+QR-code` option to *EMV Merchant-Presented QR-code*.
+
+.. image:: singapore/sg-qr-code-invoice-setting.png
+   :alt: Select EMV Merchant-Presented QR-code option
+
+Ensure that the :guilabel:`Recipient Bank` is the one you configured, as Odoo uses this field to
+generate the PayNow QR code.