Clarify that Ultimate version of IntelliJ IDEA is required / recommended

Hello,

there are two versions of IntelliJ IDEA:

• Community Edition: Free version with limited functionality
• Ultimate: Paid version (free for students, can apply here: https://www.jetbrains.com/shop/eform/students); has JPA support

It might be good to clarify in the README (in bold font) that the Ultimate version of IntelliJ IDEA is needed. Currently that does not seem to be explicitly mentioned.

Or in case the Ultimate version is not needed you can probably remove the following from the README:

Für IntelliJ ist vorab eine kostenlose Registrierung als Student notwendig.