Add documentation for known login issue with Pagure migrator

- Add known_issue_cannot_create_user.adoc with comprehensive documentation
- Document manual and automated workarounds for affected user accounts
- Add link to fedora-infrastructure ticket tracker for reporting issues
- Update navigation to include new 'Known Issues' section

Resolves: https://codeberg.org/fedora/forgejo-deployment/issues/162

modules/ROOT/nav.adoc

@@ -5,3 +5,5 @@
 * xref:admin_docs.adoc[Admin Documentation]
  ** xref:creating_a_new_org.adoc[Creating a new Organization]
  ** xref:creating_a_new_team.adoc[Creating a new Team]
+* Known Issues
+ ** xref:known_issue_cannot_create_user.adoc[Unable to Log in - "Cannot Create Account"]

modules/ROOT/pages/known_issue_cannot_create_user.adoc

@@ -0,0 +1,79 @@
+= Known Issue: Unable to Log in - "Cannot Create Account"
+
+== Purpose
+
+This document explains a known issue with the Pagure migrator where user accounts are created but not properly enabled. The issue presents itself when an affected user attempts to log in to Fedora Forge. Instead of a successful login, the user receives an error message stating that they are unable to create their account and must contact a system administrator for assistance. This occurs because the user's account has been created by the migrator but has not been finalized in the same way as a new account created via the Forgejo UI.
+
+[NOTE]
+====
+If you encounter this issue, please file a ticket on the link:https://pagure.io/fedora-infrastructure[`fedora-infrastructure` ticket tracker on Pagure] to report the problem and request assistance.
+====
+
+== Scope
+
+This document applies to Fedora Forge administrators who need to resolve login issues for users affected by the Pagure migrator. The procedures outlined here are specific to the Fedora Forge implementation.
+
+[NOTE]
+====
+This issue is specific to the Fedora Forge implementation of the Pagure migrator, as it is the only version that automatically creates user accounts. Other Forgejo instances do not exhibit this behavior as their migrators do not have this functionality.
+====
+
+== Prerequisites
+
+* *Administrator Privileges:* The user must possess administrator privileges on Fedora Forge to perform these procedures.
+* *Access to Fedora System:* For the automated workaround, access to a Fedora system with Python installed is required.
+
+== Procedure
+
+=== Manual Workaround (For Individual Users)
+
+An administrator can manually fix this issue for a single user by performing the following steps in the Forgejo UI:
+
+. *Log in as Administrator:*
+.. Log in as a Fedora Forge administrator to Fedora Forge.
+
+. *Navigate to Admin Panel:*
+.. Navigate to the Admin Panel.
+
+. *Access User Management:*
+.. Go to the User Management section.
+
+. *Locate and Edit User Account:*
+.. Find and click on the user's account to open their settings.
+
+. *Update User Account:*
+.. Without making any changes, click the *"Update user account"* button to save changes.
+
+=== Automated Workaround (For Multiple Users)
+
+For administrators dealing with a large number of affected users, the `update_users.py` script provides an automated solution. This script automates the tedious manual process of visiting each user's edit page and saving changes, ensuring that all migrated accounts are properly enabled.
+
+==== Step 1: Open a Terminal
+
+Start by opening a new terminal window on your Fedora system.
+
+==== Step 2: Create a Python Virtual Environment
+
+It's a best practice to use a virtual environment to isolate the script's dependencies from your system's Python packages.
+
+==== Step 3: Install Required Dependencies
+
+Install the necessary Python packages for the script to function properly.
+
+==== Step 4: Run the Update Script
+
+Execute the `update_users.py` script to automatically fix all affected user accounts.
+
+== Verification
+
+* Confirm that affected users can now successfully log in to Fedora Forge.
+* Verify that user accounts are properly enabled and functional.
+* Test that users can access their repositories and perform normal operations.
+
+== Troubleshooting
+
+If users continue to experience login issues after applying these workarounds:
+
+* Verify that the user account exists in the Fedora Forge user management system.
+* Check that the account has been properly activated.
+* Contact the Fedora Infrastructure team if the issue persists.