Populate the dev-env help documentation with the supported PHP versions.

src/lib/dev-environment/dev-environment-cli.ts

@@ -858,6 +858,8 @@ export function processVersionOption( value: unknown ): string {
 	return value?.toString() ?? '';
 }
 
+const phpVersionsSupported: string = Object.keys(DEV_ENVIRONMENT_PHP_VERSIONS).join(', ');
+
 export function addDevEnvConfigurationOptions( command: Args ): Args {
 	// We leave the third parameter to undefined on some because the defaults are handled in preProcessInstanceData()
 	return command
@@ -905,7 +907,7 @@ export function addDevEnvConfigurationOptions( command: Args ): Args {
 		)
 		.option(
 			'php',
-			'Manage the version of PHP. Accepts a string value for minor versions (8.x). Defaults to the most recent version of PHP.',
+			`Manage the version of PHP. Accepts a string value for minor versions: ${phpVersionsSupported}.`,
 			undefined,
 			processVersionOption
 		)