Update README

Author: ebln

README.md

@@ -1,6 +1,6 @@
 ebln/phpstan-factory-mark
 =========================
 
-Provides the interface needed for `ebln/phpstan-factory-rule`.
+Provides the interface needed for [`ebln/phpstan-factory-rule`](https://github.com/ebln/phpstan-factory-rule).
 
 This is needed because the interface will reside in production code, while the phpstan rule is usually only required for development.