Document rclone storage backend

Cloud-Tier.md

@@ -50,9 +50,14 @@ Compared to direct S3 storage, this is both faster and cheaper!
 1. Use `volume.tier.download` in `weed shell` to move volumes to the local cluster.
 
 ## Configuring Storage Backend
-(Currently only s3 is developed. More is coming soon.)
 
-Multiple s3 buckets are supported. Usually you just need to configure one backend.
+The following storage backends are currently supported:
+- S3
+- Rclone
+
+### S3
+
+Multiple S3 buckets are supported. Usually you just need to configure one backend.
 
 ```
 # The storage backends are configured on the master, inside master.toml
@@ -75,6 +80,26 @@ Multiple s3 buckets are supported. Usually you just need to configure one backen
 
 ```
 
+### Rclone
+
+Here's an example of a configuration for an Rclone storage backend:
+
+```
+[storage.backend]
+	[storage.backend.rclone.default]
+	enabled = true
+	remote_name = "my-onedrive"
+```
+
+Where `my-remote` must correspond to what's configured in `~/.config/rclone/rclone.conf`:
+```
+[my-onedrive]
+type = onedrive
+...
+```
+
+### Configuration
+
 After changing the master config, you need to **restart the volume servers** so that they pull the updated configuration
 from the master. If you forget to do this, you'll get an error message about no storage backends being configured.