RFR: Update the readme to include IntelliJ setup instructions [v2]

[Erik Helin]

On Tue, 2 Feb 2021 14:32:57 GMT, Robin Westberg <rwestberg at openjdk.org> wrote:

>> README.md line 226:
>> 
>>> 224: IDE when working on Skara you can simply open the root folder and the project
>>> 225: should be automatically imported. You will need to configure a Platform SDK that
>>> 226: is JDK 14 or above. Either set this up manually, or [build](#building) once from
>> 
>> We are using JDK 15 now ��
>
> Sure, but the `Building` section still says that 14 or later is needed, and I guess that is still actually true. :)

Ok, sure, I agree.

-------------

PR: https://git.openjdk.java.net/skara/pull/998