docs(config): explain that `autoupdate` doesn't work when installed with a package manager (#9092)

packages/web/src/content/docs/config.mdx

@@ -425,6 +425,7 @@ OpenCode will automatically download any new updates when it starts up. You can
 ```
 
 If you don't want updates but want to be notified when a new version is available, set `autoupdate` to `"notify"`.
+Notice that this only works if it was not installed using a package manager such as Homebrew.
 
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