Merge pull request #4 from useblacksmith/v2/update-readme

begin-testbox: update readme for v2 actions

Author: aayushshah15

README.md

@@ -1,6 +1,6 @@
 # begin-testbox
 
-First half of the Blacksmith Testbox action pair. This action runs right after `actions/checkout` and before your dependency installation steps. It installs an SSH public key for remote access, ensures `rsync` is available, and phones home to the Testbox API with a `hydrating` status.
+First half of the Blacksmith Testbox action pair. This action runs right after `actions/checkout` and before your dependency installation steps. It discovers configuration from the VM metadata service, phones home to the Testbox API with a `hydrating` status, installs the SSH public key returned by the API, and ensures `rsync` is available.
 
 Pair this with [useblacksmith/run-testbox](https://github.com/useblacksmith/run-testbox), which runs after your setup steps to signal the testbox is ready and keep the runner alive until idle timeout.
 
@@ -11,34 +11,29 @@ steps:
   - uses: actions/checkout@v4
 
   - name: Begin Testbox
-    uses: useblacksmith/begin-testbox@v1
+    uses: useblacksmith/begin-testbox@v2
     with:
       testbox_id: ${{ inputs.testbox_id }}
-      testbox_token: ${{ inputs.testbox_token }}
-      idle_timeout: ${{ inputs.idle_timeout }}
-      api_url: ${{ inputs.api_url }}
-      ssh_public_key: ${{ inputs.ssh_public_key }}
 
   # --- your setup steps here ---
   - uses: actions/setup-node@v4
   - run: npm ci
   # --- end setup ---
 
   - name: Run Testbox
-    uses: useblacksmith/run-testbox@v1
-    with:
-      testbox_id: ${{ inputs.testbox_id }}
-      testbox_token: ${{ inputs.testbox_token }}
-      idle_timeout: ${{ inputs.idle_timeout }}
-      api_url: ${{ inputs.api_url }}
+    uses: useblacksmith/run-testbox@v2
 ```
 
 ## Inputs
 
 | Input | Required | Default | Description |
 |-------|----------|---------|-------------|
 | `testbox_id` | yes | | Testbox session ID |
-| `testbox_token` | yes | | Bearer token for phone-home authentication |
-| `idle_timeout` | no | `10` | Idle timeout in minutes |
-| `api_url` | yes | | Backend API URL for phone-home callbacks |
-| `ssh_public_key` | no | `''` | SSH public key to install for access |
+
+## How it works
+
+1. Reads `installationModelID`, `backendURL`, and `stickyDiskToken` from the VM metadata service
+2. Phones home to `/api/testbox/phone-home` with `hydrating` status, authenticated via the sticky disk token
+3. Receives `ssh_public_key` and `idle_timeout` from the API response
+4. Writes state to `/tmp/.testbox/` for `run-testbox` to consume
+5. Installs the SSH public key and ensures `rsync` is available