add htpasswd note

Author: nicktrn

docs/self-hosting/docker.mdx

@@ -212,6 +212,8 @@ The default settings for the registry are:
 
 You should change these before deploying to production, especially the password. You can find more information about how to do this in the official [registry docs](https://github.com/distribution/distribution/blob/735c161b53e7faf81a21ba94c55ac9edee081cd9/docs/deploying.md#native-basic-auth).
 
+**Note:** This will require modifying the default `.htpasswd` file located at `./hosting/docker/registry/auth.htpasswd` of the repo root.
+
 ### Logging in
 
 When self-hosting, builds run locally. You will have to login to the registry on every machine that runs the `deploy` command. You should only have to do this once: