Add version info in README

Author: codeliner

README.md

@@ -1,3 +1,10 @@
 # php-json-schema
 
 Event Engine JSON Schema PHP Package
+
+## Versions
+
+- 1.x uses method return type hints to detect ImmutableRecord property types
+    - Use this version in PHP 7.2 - PHP 7.3 environments
+- 2.x makes use of PHP 7.4 property type hints 
+    - Use this version in  >= PHP 7.4 environments