doc: add initial README with usage instructions and environment variables

Author: liogate

README.md

@@ -0,0 +1,42 @@
+# rclone
+
+A tool for managing files on cloud storage.
+
+## Usage
+
+```sh
+docker run --rm -it -v $(pwd)/rclone.conf:/data/rclone.conf:ro \
+    -e RCLONE_SOURCE=my-source \
+    -e RCLONE_DESTINATION=my-destination \
+    -e RCLONE_ARGS="--checksum --max-age 12h --delete-excluded" \
+    skyloud/rclone sync
+```
+
+## Entrypoint Argument
+
+| Argument  | Description                       |
+|-----------|-----------------------------------|
+| `command` | rclone command (e.g., copy, sync) |
+
+## Environment Variables
+
+| Variable             | Description                               |
+|----------------------|-------------------------------------------|
+| `RCLONE_CONFIG`      | Path to rclone config file                |
+| `RCLONE_SOURCE`      | Source location for rclone operation      |
+| `RCLONE_DESTINATION` | Destination location for rclone operation |
+| `RCLONE_ARGS`        | Additional arguments for rclone           |
+| `HEARTBEAT_URL`      | URL for sending heartbeat status          |
+
+
+## Example
+
+```sh
+RCLONE_CONFIG=/data/rclone.conf
+RCLONE_SOURCE=my-source
+RCLONE_DESTINATION=my-destination
+RCLONE_ARGS='--checksum'
+HEARTBEAT_URL=https://...
+```
+
+See [rclone documentation](https://rclone.org/docs/) for more details.