Add migrate command to docs (#8842)

* Add migrate command to docs

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Link to CLI

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Clarify idempotence

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Sneak in convert command

Signed-off-by: jolheiser <john.olheiser@gmail.com>

docs/content/doc/help/faq.en-us.md

@@ -42,6 +42,7 @@ Also see [Support Options]({{< relref "doc/help/seek-help.en-us.md" >}})
   * [SSH Common Errors](#ssh-common-errors)
 * [Missing releases after migration repository with tags](#missing-releases-after-migrating-repository-with-tags)
 * [LFS Issues](#lfs-issues)
+* [How can I create users before starting Gitea](#how-can-i-create-users-before-starting-gitea)
 
 
 ## Difference between 1.x and 1.x.x downloads
@@ -272,3 +273,6 @@ Check the value of `LFS_HTTP_AUTH_EXPIRY` in your `app.ini` file.
 By default, your LFS token will expire after 20 minutes. If you have a slow connection or a large file (or both), it may not finish uploading within the time limit. 
 
 You may want to set this value to `60m` or `120m`.
+
+## How can I create users before starting Gitea
+Gitea provides a sub-command `gitea migrate` to initialize the database, after which you can use the [admin CLI commands]({{< relref "doc/usage/command-line.en-us.md" >}}) to add users like normal.

docs/content/doc/usage/command-line.en-us.md

@@ -281,3 +281,10 @@ provided key. You should also set the value
 NB: opensshd requires the gitea program to be owned by root and not
 writable by group or others. The program must be specified by an absolute
 path.
+
+#### migrate
+Migrates the database. This command can be used to run other commands before starting the server for the first time.  
+This command is idempotent.
+
+#### convert
+Converts an existing MySQL database from utf8 to utf8mb4.