add notes to create an emergency user (#1703)

* add notes to create an emergency user

* Sentence-case index.md

* Merge content from Plone 5 docs in https://5.docs.plone.org/manage/deploying/zope.html#adding-users-from-command-line

* Move the how to to the Admin guide section

* Add some more examples and clarifications

* Clarify and rework the docs for adding a Zope manager user

* Update docs/backend/index.md

* rename file, update metadata

* Restore users-groups

See #1410

* Polish up Zope manager users (#1867)

* Polish up Zope manager users

* Consistent indents of 4 spaces

---------

Co-authored-by: Steve Piercy <[email protected]>
Co-authored-by: ale-rt <[email protected]>
Co-authored-by: David Glick <[email protected]>

docs/admin-guide/index.md

@@ -30,6 +30,7 @@ install-pip
 
 run-plone
 add-site
+zope-manager-users
 configure-zope
 add-ons
 export-import

docs/admin-guide/zope-manager-users.md

@@ -0,0 +1,109 @@
+---
+myst:
+  html_meta:
+    "description": "How to create a Zope manager user in an existing Zope instance"
+    "property=og:description": "How to create a Zope manager user in an existing Zope instance"
+    "property=og:title": "Zope manager users"
+    "keywords": "Plone, Zope, users, admin user, emergency user, administration, pip, buildout"
+---
+
+(admin-guide-zope-manager-user-label)=
+
+# Zope manager users
+
+This guide explains how to add a Zope user with the "manager" role—called a "Zope manager user"—to an existing Zope instance.
+
+Zope manager users have full access to the whole Zope instance.
+
+Some installation methods automatically create a Zope manager user named `admin` for you already.
+
+There are multiple reasons why you might need to add a Zope manager user, including the following.
+
+-   Your installation method did not create one.
+-   You lost access to your instance.
+-   You inherited a project without proper documentation.
+
+```{note}
+If you need to regain access to your instance, this user is also referred to as an "emergency user" in this context only.
+
+The emergency user is a superuser with full access to the Zope instance.
+It is not limited to a specific Plone site.
+Please be aware of the security implications.
+Consider changing the passwords of the existing Zope manager users after you regain access to your instance.
+```
+
+(admin-guide-add-a-new-zope-manager-user-label)=
+
+## Add a new Zope manager user
+
+There are multiple methods to create a Zope manager user.
+The method depends on how you created and manage your Zope instance, either via {term}`buildout` or {term}`pip`.
+
+```{important}
+If you are running a standalone instance, you must stop it before adding the user.
+```
+
+(admin-guide-adduser-instance-command-label)=
+
+### `adduser` instance command
+
+If your site was installed with `buildout` and `plone.recipe.zope2instance`, you can add a Zope manager user via the instance script.
+
+Run the following command.
+
+```shell
+bin/instance adduser username password
+```
+
+The name of the instance script might vary based on your installation.
+Replace `username` and `password` with the desired values.
+
+If the command is successful, then it will return the following console output.
+
+```console
+Created user: username
+```
+
+When you run the script, if the user already exists:
+
+-   No user will be created.
+-   The password will not be changed. 
+-   The command will return a message such as the following.
+
+    ```console
+    Created user: None
+    ```
+
+(admin-guide-addzopeuser-command-label)=
+
+### `addzopeuser` script
+
+For `pip` based installations, you will have a script called `addzopeuser` in the {file}`bin` directory of your virtual environment.
+The `addzopeuser` script might also be available in `buildout` based installations.
+
+Run the following command.
+
+```shell
+$ .venv/bin/addzopeuser -c path/to/etc/zope.conf username password
+```
+
+The `addzopeuser` script and {file}`zope.conf` locations might vary based on your installation.
+Replace `username` and `password` with the desired values.
+
+If the command is successful, then it will return the following console output.
+
+```console
+User username created.
+```
+
+When you run the script, if the user already exists:
+
+-   No user will be created.
+-   The password will not be changed.
+-   The command will return a message such as the following.
+
+    ```console
+    Got no result back. User creation may have failed.
+    Maybe the user already exists and nothing is done then.
+    Or the implementation does not give info when it succeeds.
+    ```