[DOCS] Rework the development deps section in CONTRIBUTING.md (#1354)

CONTRIBUTING.md

@@ -53,18 +53,23 @@ first before investing a lot of time in writing code.
 
 ## Install the development dependencies
 
-To install the development dependencies (PHPUnit and PHP_CodeSniffer), please
-run the following commands:
+To install the most important development dependencies, please run the following
+command:
 
-```shell
+```bash
 composer install
-composer require --dev slevomat/coding-standard:^4.0
 ```
 
-Note that the development dependencies (in particular, for PHP_CodeSniffer)
-require PHP 7.0 or later. The second command installs the PHP_CodeSniffer
-dependencies and should be omitted if specifically testing against an earlier
-version of PHP, however you will not be able to run the static code analysis.
+We also have some optional development dependencies that require higher PHP
+versions than the lowest PHP version this project supports. Hence they are not
+installed by default.
+
+To install these, you will need to have [PHIVE](https://phar.io/) installed.
+You can then run the following command:
+
+```bash
+phive install
+```
 
 ## Unit-test your changes