Add rgw_swift_enforce_content_length parameter

* Some tempest tests use accept-ranges header
  which is added by this param

Change-Id: Ideb3883ab89a0c3d3defbb93b3bcc1208f377fc3
Closes-Bug: #PROD-24333 (PROD:24333)
diff --git a/README.rst b/README.rst
index 825f128..dcd9462 100644
--- a/README.rst
+++ b/README.rst
@@ -453,6 +453,7 @@
         swift:
           versioning:
             enabled: true
+          enforce_content_length: true
 
 
 Ceph setup role