extend comment about backward compatibility

src/lib/cfa/ntp_conf.rb

@@ -397,6 +397,37 @@ def options
         res = augeas_options.map { |option| option[:value] }
         # backward compatibility with old lense that set value ip restriction
         # instead of address
+        # for old lenses data can look like:
+        #   line in configuration file:
+        #     restrict -4 default nofail
+        #   augeas tree:
+        #     key:       restrict
+        #     value:     -4
+        #     action[1]: default
+        #     action[2]: nofail
+        #
+        #   line in configuration file:
+        #     restrict default nofail
+        #   augeas tree:
+        #     key:       restrict
+        #     value:     default
+        #     action[1]: nofail
+        #
+        # with new lense value is always address like:
+        #   line in configuration file:
+        #     restrict -4 default nofail
+        #   augeas tree:
+        #     key:       restrict
+        #     value:     default
+        #     action[1]: nofail
+        #     ipv4:      nil
+        #
+        #   line in configuration file:
+        #     restrict default nofail
+        #   augeas tree:
+        #     key: restrict
+        #     value: default
+        #     action[1]: default
         res.shift if ["-6", "-4"].include?(value)
 
         res