update README.md

README.md

@@ -538,6 +538,19 @@ Or:
 $ make triq t=cow_http_hd:prop_parse_accept
 ```
 
+Xref plugin
+------------
+
+This plugin is available by default. It adds the following
+target:
+
+`xref` Erlang Xref Runner (inspired in rebar's rebar_xref)
+
+The `XREF_CONFIG` variable specifies the location of the
+configuration file which holds the checks to be applied.
+If there is no `xref.config` all `xref` checks will be
+applied to the binaries located in the `/ebin` directory.
+
 Contributing
 ------------