Adds notes for suggested packages in documentation

[froschdesign]

Suggested packages are:

zend-validator/composer.json

Lines 35 to 45 in e633fe6

	"suggest": {
	"psr/http-message": "psr/http-message, required when validating PSR-7 UploadedFileInterface instances via the Upload and UploadFile validators",
	"zendframework/zend-db": "Zend\\Db component, required by the (No)RecordExists validator",
	"zendframework/zend-filter": "Zend\\Filter component, required by the Digits validator",
	"zendframework/zend-i18n": "Zend\\I18n component to allow translation of validation error messages",
	"zendframework/zend-math": "Zend\\Math component, required by the Csrf validator",
	"zendframework/zend-i18n-resources": "Translations of validator messages",
	"zendframework/zend-servicemanager": "Zend\\ServiceManager component to allow using the ValidatorPluginManager and validator chains",
	"zendframework/zend-session": "Zend\\Session component, ^2.8; required by the Csrf validator",
	"zendframework/zend-uri": "Zend\\Uri component, required by the Uri and Sitemap\\Loc validators"
	},

Related to laminas/documentation#7

[michalbundyra]

Thanks, @froschdesign!