Readme updated

Author: spirali

parley/tests/README.md

@@ -13,4 +13,27 @@ If you think that everything is ok, you can start tests as follows:
 $ PARLEY_TEST="accept" cargo test
 ```
 
-It will update snapshots of the failed tests.
+It will update snapshots of the failed tests.
+
+## Usage of xtask when test fails
+
+After some tests fails, you may run the following for generating kompari HTML report:
+
+```bash
+cargo xtask report
+```
+
+or start an interactive test blessing
+
+```bash
+cargo xtask review
+```
+
+## Detect dead snapshots
+
+The following command shows snapshots that are not used in any test. The command also allows to delete such snaphosts.
+
+```bash
+cargo xtask dead-snapshots 
+```
+