feat(adminmanual): Add 26 upgrade docs

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

Author: ChristophWurst

admin_manual/configuration_server/email_configuration.rst

@@ -1,3 +1,5 @@
+.. _email-config:
+
 =====
 Email
 =====
@@ -29,6 +31,8 @@ Sendmail when your mail server is on the same machine as Nextcloud.
    drop-in Sendmail replacement such as Postfix, Exim, or Courier. All of
    these include a ``sendmail`` binary, and are freely-interchangeable.
 
+.. _email-smtp-config:
+
 Configuring an SMTP server
 --------------------------
 

admin_manual/installation/nginx.rst

@@ -1,3 +1,5 @@
+.. _nginx-config:
+
 ===================
 NGINX configuration
 ===================

admin_manual/release_notes/index.rst

@@ -15,6 +15,7 @@ These sub pages will cover the most important changes in Nextcloud, as well as s
    :maxdepth: 1
 
    upgrade_to_27.rst
+   upgrade_to_26.rst
 
 Changelog
 ---------

admin_manual/release_notes/upgrade_to_26.rst

@@ -0,0 +1,19 @@
+=======================
+Upgrade to Nextcloud 26
+=======================
+
+System requirements
+-------------------
+
+* PHP 8.2 is now supported, but 8.1 is recommended.
+* PHP7.4 is no longer supported.
+
+System email
+------------
+
+The software component to send system emails (notifications, invites, password reset, etc) had to be replaced. The new library should work without any changes out of the box for most setups. Only NTLM/Exchange is kown to be no longer supported. See :ref:`email-smtp-config`.
+
+Web server configuration
+------------------------
+
+* The recommended :ref:`nginx configuration<nginx-config>` changed.