explain how to set per-directory TTL using the s3 api

S3-API-FAQ.md

@@ -52,3 +52,40 @@ rclone lsf seaweedfs:my-bucket/dir
 ```
 
 If the directory `dir` exists in `my-bucket`, the orphaned metadata will be cleaned up. Note that due to slight API usage differences, `rclone ls` does not trigger cleanup, but `rclone lsf` will. 
+
+
+## Setting TTL
+
+It is possible to set a TTL for a specific directory using the S3 API. They are set using [`PutBucketLifecycleConfiguration`](https://docs.aws.amazon.com/AmazonS3/latest/API/API_PutBucketLifecycleConfiguration.html).
+
+Example of a JSON configuration is below.  It is an equivalent of calling the following with `weed shell`.
+```
+fs.configure -locationPrefix  /buckets/f341868e-baff-4e20-896a-08bc148e32f9/my-directory-whose-files-will-expire-in-20-days -ttl 20d -apply
+```
+:
+
+```
+{
+  "Rules": [
+    {
+      "Status": "Enabled",
+      "Filter": {
+        "Prefix": "my-directory-whose-files-will-expire-in-20-days"
+      },
+      "Expiration": {
+        "Days": 20d
+      }
+    }
+  ]
+}
+```
+Save that in a `.json` file and call it, for example, via the `aws` cli:
+
+```
+BUCKET_NAME=f341868e-baff-4e20-896a-08bc148e32f9
+aws --endpoint-url http://127.0.0.1:8333 s3api put-bucket-lifecycle-configuration --bucket $BUCKET_NAME --lifecycle-configuration "file://lifecycle_policy.json"
+```
+
+Note that you don't need to add the part `/buckets/$BUCKET_NAME` in the configurations "Filter.Prefix" (contrary to using `fs.configure`, this is taken care of for you in the S3 API.
+
+