[IntelliJ] Add note on Imports

What happened?

I have activated palantir java format:

This does not change the code style configured in the IDE:

When executing "optimize imports", the configured style is followed.

• I think, the plugin needs to change the code style to "Default" or - even better - to "palantir" in the IDE settings, to be really transparent, about the import statements

What did you want to happen?

When executing "optimize imports", the palantir-style is followed

General wishes:

• Write down in README.md about the style rules for imports. Maybe a link to the Google Java Style (https://google.github.io/styleguide/javaguide.html#s3.3-import-statements) would be enough?
• Advanced: Supply checkstyle rules to check for palantir's import rules (so that one can use the rules in the CI to check)

Start by reviewing README.md and the IntelliJ integration responsible for import optimization and IDE code-style settings. Clarify whether the intended scope is the plugin behavior, documentation of import rules, or checkstyle support. Done means the selected scope is implemented and verified against the stated Palantir import style; the issue has no named tests or entry points.