Update installation instructions for Web UI

Recent versions of SmartOS ship with uiadm.

Author: nshalman

docs/web-interface.md

@@ -15,22 +15,12 @@ configuration on an instance or image that causes errors in the UI.
 
 ## Installation
 
-To install the web interface, download and run the installer.
+You can use `uiadm` to install the web interface:
 
 ```sh
-curl -O https://us-central.manta.mnx.io/Joyent_Dev/public/SmartOS/ui-installer.sh
-bash ./ui-installer.sh
+uiadm install latest
 ```
 
-Or, the quick and dirty way:
-
-<!-- markdownlint-disable line-length -->
-
-```sh
-curl https://us-central.manta.mnx.io/Joyent_Dev/public/SmartOS/ui-installer.sh | bash
-```
-<!-- markdownlint-enable line-length -->
-
 ## Accessing the Web UI
 
 The UI is available on port 4443. The installer will print out the URL