diff --git a/plugins/disk/btrfs_device_usage b/plugins/disk/btrfs_device_usage
index dd62d44d..d422120a 100755
--- a/plugins/disk/btrfs_device_usage
+++ b/plugins/disk/btrfs_device_usage
@@ -16,13 +16,27 @@ Must be run as root.
 [btrfs_device_usage]
 user root
 
+You can optionaly configure the warning and critical limits for byte and
+percentage graphs. By default percent_warning is set to 95 and percent_critical
+is 98. For the byte-graphs there are no default limits set. You can set the
+limits either for the entire graph (byte_ percent_) or per individual filesystem
+using it's UUID (replace minus with underscore). The individual values take
+precedence over the general ones. See the following example:
+
+btrfs_device_usage]
+user root
+env.byte_warning 400300200100
+env.percent_critical 97
+env.percent_10164f3f_6670_4982_a941_bffb50d27f29_warning 23
+env.byte_10164f3f_6670_4982_a941_bffb50d27f29_critical 5000000000
+
 =head2 DEFAULT CONFIGURATION
 
 =head1 BUGS
 
 =head1 AUTHOR
 
-2019, HaseHarald
+2019-2021, HaseHarald
 
 =head1 MAGIC MARKERS