docs: local-file Genericode import flow (#246) (#249)

* Initial plan

* docs: clarify genericode import flow

Agent-Logs-Url: https://github.com/alyf-de/eu_einvoice/sessions/532d9d71-ff00-447c-b7cd-96c2eb9d8e48



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(cherry picked from commit 0bb4808)

Co-authored-by: Copilot <198982749+Copilot@users.noreply.github.com>
Co-authored-by: barredterra <14891507+barredterra@users.noreply.github.com>

Author: 3 people

README.md

@@ -31,7 +31,7 @@ Please use a branch (`MAJOR_VERSION`) that matches the major version of ERPNext
 
 E-invoices rely on common codes that describe the content of the invoice. E.g. "C62" is used for the UOM "One" and "ZZZ" is used for a mutually agreed mode of payment.
 
-Common codes are part of a code list. You'll need to import the code lists and map the codes you need to the corresponding ERPNext entities. Please use the "Import Genericode" button in **Code List** and paste the URL linked below.
+Common codes are part of a code list. You'll need to import the code lists and map the codes you need to the corresponding ERPNext entities. Please use the "Import Genericode" button in **Code List**, download the linked XML file first, and then upload it from your computer. Importing Genericode directly from a remote URL no longer works in recent ERPNext versions.
 
 Code List | Mapped DocType | Default Value
 ----------|----------------|--------------