Fix markdown link formatting in README.md

Author: macintoshplus

README.md

@@ -35,7 +35,7 @@ Installation system support:
 | PECL     | no  :x:                |
 | PIE      | yes :white_check_mark: |
 
-To install the extension, use PIE](https://github.com/php/pie) (PHP Installer Extension) with a command like:
+To install the extension, use [PIE](https://github.com/php/pie) (PHP Installer Extension) with a command like:
 
 ```bash
 pie install php-win-ext/rar