Create faq.md (#366)

Author: staabm

README.md

@@ -101,3 +101,4 @@ includes:
 - [MySQL Support](https://github.com/staabm/phpstan-dba/blob/main/docs/mysql.md)
 - [PGSQL Support](https://github.com/staabm/phpstan-dba/blob/main/docs/pgsql.md)
 - [Reflector Overview](https://github.com/staabm/phpstan-dba/blob/main/docs/reflectors.md)
+- [How to analyze a PHP 7.x codebase?](https://github.com/staabm/phpstan-dba/blob/main/docs/faq.md)

docs/faq.md

@@ -0,0 +1,5 @@
+# Frequently asked questions 
+
+## how to analyze a php7.x codebase?
+
+Make sure to either define the target platform version in your `composer.json` or define your target [php version in your phpstan-config](https://phpstan.org/config-reference#phpversion).