[README] fix ecs.php link

build/target-repository/README.md

@@ -189,4 +189,4 @@ dump_node($node, 1);
 
 Rector uses [nikic/php-parser](https://github.com/nikic/PHP-Parser/), built on technology called an *abstract syntax tree* (AST). An AST doesn't know about spaces and when written to a file it produces poorly formatted code in both PHP and docblock annotations. **That's why your project needs to have a coding standard tool** and a set of formatting rules, so it can make Rector's output code nice and shiny again.
 
-We're using [ECS](https://github.com/symplify/easy-coding-standard) with [this setup](ecs.php).
+We're using [ECS](https://github.com/symplify/easy-coding-standard) with [this setup](https://github.com/rectorphp/rector-src/blob/main/ecs.php).