Update app/README.md

Fix documentation link to CLI reference

Author: bzz

catboost/app/README.md

@@ -1,4 +1,4 @@
 ### Command line utility
 Command line utility can be used in fit, calc and fstr modes.
 
-All details about utility usage can be found in [documentation](https://api-trunk-d-guitarman-d-tech2.dev1f.tech.yandex.com:5555/catboost/doc/dg/concepts/cli-reference-docpage/)
+All details about utility usage can be found in [documentation](https://tech.yandex.com/catboost/doc/dg/concepts/cli-reference-docpage/)