README: Add description for "[default_]source_root"

diff --git a/README.md b/README.md
index 3025b2eac8ff74e240a81914cc35b536ee8024f8..bfbd7250fa069017a55cfab74f0319ac051782b2 100644 (file)
--- a/README.md
+++ b/README.md
@@ -67,6 +67,13 @@ System host name. Default: file name.
 
 Remote user. Default: `root`.
 
+### [default_]source_root
+
+Remote *root* directory, must end with a slash ("/") character! Default: "/".
+
+When saving the whole (remote) system ("/"), default excludes are set up
+automatically, which exclude standard system directories like /sys and /proc.
+
 ### [default_]target
 
 Local backup directory. The backup of each system is stored in a folder named