fix: describe registry-url behavior accurately (writes to $RUNNER_TEMP)

Author: fengmk2

action.yml

@@ -28,7 +28,7 @@ inputs:
     description: "Path to lock file for cache key generation. Auto-detected if not specified."
     required: false
   registry-url:
-    description: "Optional registry to set up for auth. Will set the registry in a project level .npmrc and set up auth to read in from env.NODE_AUTH_TOKEN."
+    description: "Optional registry to set up for auth. Will write .npmrc in $RUNNER_TEMP with registry and auth config, and set NPM_CONFIG_USERCONFIG to point npm at it. Auth token is read from env.NODE_AUTH_TOKEN."
     required: false
   scope:
     description: "Optional scope for authenticating against scoped registries. Will fall back to the repository owner when using the GitHub Packages registry (https://npm.pkg.github.com/)."