Clarify autoinstall file naming: user-data and meta-data have no extensions

ubuntu-autoinstall/README.md

@@ -24,12 +24,17 @@ Replaces MAAS for small batches. Fully autonomous after USB boot.
 
 Create these two files in the **root of the USB's writable partition**:
 
-**`user-data`**
-```
-[paste entire contents of autoinstall.yaml here]
+**`user-data`** — copy `autoinstall.yaml` and rename it to `user-data` (no extension):
+```bash
+cp autoinstall.yaml /media/usb/user-data
 ```
 
-**`meta-data`** (can be empty)
+**`meta-data`** — create an empty file literally named `meta-data` (no extension):
+```bash
+touch /media/usb/meta-data
+```
+
+Optional content for `meta-data`:
 ```yaml
 instance-id: iid-ironlegion01
 local-hostname: ubuntu