Make PHAR the prefered way to install PHPUnit (#882)

Author: A-O-Emmanuel

docs/INSTALLATION.md

@@ -83,16 +83,51 @@ Install [Composer](https://getcomposer.org) following your devices OS [installat
 
 ## Install PHPUnit
 
-### Via Composer
+### Via PHP Archive (PHAR)
+
+The easiest way to use PHPUnit for Exercism exercises is downloading a distribution that is packaged as a PHP Archive (PHAR), which is also the recommended way to use PHPUnit.
+Store the PHAR where you stored the `exercism` CLI to run PHPUnit from wherever you are.
 
-PHPUnit version 10 can be installed globally via [Composer](https://getcomposer.org), using the following command:
+You can download a release of PHPUnit packages as a PHP archive:
 
 ```shell
-composer global require phpunit/phpunit ^10.5
+wget -O phpunit.phar https://phar.phpunit.de/phpunit-10.phar
+```
+
+Then make the downloaded file executable:
+
+```shell
+chmod +x phpunit.phar
 ```
 
-Please make sure you install version 10.5 or later.
+And move it to the same location as you moved the `exercism` CLI, naming the command `phpunit`:
+
+```shell
+mv phpunit.phar ~/bin/phpunit
+```
+
+Now you can run `phpunit` from wherever you are, as shown in the [PHP track testing docs](https://exercism.org/docs/tracks/php/tests):
+
+```shell
+phpunit --version
+```
 
-### Manual installation
+The output should look like this:
+
+```
+PHPUnit 10.5.45 by Sebastian Bergmann and contributors.
+
+```
+
+
+You can also follow the official [Installing PHPUnit instructions](https://docs.phpunit.de/en/10.5/installation.html#installing-phpunit) to install PHPUnit.
+
+### Via Composer
+
+PHPUnit version 10 can also be installed globally via [Composer](https://getcomposer.org), using the following command:
+
+```shell
+composer global require phpunit/phpunit ^10.5
+```
 
-If you are not using Composer package manager, follow the official [Installing PHPUnit instructions](https://docs.phpunit.de/en/10.5/installation.html#installing-phpunit).
+Please make sure you install version 10.5 or later.