chore: Adds suggest in composer.json.

Author: gustavofreze

composer.json

@@ -47,6 +47,9 @@
         "phpunit/phpunit": "^9.5",
         "squizlabs/php_codesniffer": "^3.7"
     },
+    "suggest": {
+        "ext-gmp": "Enables faster math with arbitrary-precision integers using GMP."
+    },
     "scripts": {
         "phpcs": "phpcs --standard=PSR12 --extensions=php ./src",
         "phpmd": "phpmd ./src text phpmd.xml --suffixes php --ignore-violations-on-exit",