Updates to the 'CLion Integration' section in ClangFormat docs

This commit updates the 'CLion Integration' section in ClangFormat docs.
Key changes:
- clang-format is enabled automatically when there is a config file;
- formatting now works for indentations;
- if clang-format is enabled without a config file, CLion suggests creating it based on the IDE settings or uses the LLVM style by default.

Patch by Marina Kalashina!

Reviewers: sylvestre.ledru, ilya-biryukov

Reviewed By: ilya-biryukov

Subscribers: ilya-biryukov, klimek, MyDeveloperDay, sammccall, gribozavr2

Differential Revision: https://reviews.llvm.org/D80721