Add minium JDK requirements

index.html

@@ -55,6 +55,11 @@ deployment environments.
 
 All avaible features, modules and their maven/gradle artifact names are described in [the Modules section of the reference documentation](http://docs.spring.io/spring-framework/docs/current/spring-framework-reference/html/overview.html#overview-modules).
 
+## Minimum requirements
+
+* JDK 6+ for Spring Framework 4.x
+* JDK 5+ for Spring Framework 3.x
+
 <span id="quick-start"></span>
 ## Quick Start