chore: separate install docs (#3859)

docs/admin/upgrade.md

@@ -0,0 +1,43 @@
+# Upgrade
+
+This article walks you through how to upgrade your Coder server.
+
+<blockquote class="danger">
+  <p>
+  Prior to upgrading a production Coder deployment, take a database snapshot since
+  Coder does not support rollbacks.
+  </p>
+</blockquote>
+
+To upgrade your Coder server, simply reinstall Coder using your original method
+of [install](../install).
+
+## Via install.sh
+
+If you installed Coder using the `install.sh` script, re-run the below
+command on the host:
+
+```console
+curl -L https://coder.com/install.sh | sh
+```
+
+The script will unpack the new `coder` binary version over the one currently installed.
+Next, you can restart Coder with the following command (if running it as a system
+service):
+
+```console
+systemctl restart coder
+```
+
+## Via docker-compose
+
+If you installed using `docker-compose`, run the below command to upgrade the
+Coder container:
+
+```console
+docker-compose pull coder && docker-compose up coder -d
+```
+
+## Up Next
+
+- [Learn how to configure Coder](./configure.md).