Adding 'CLion integration' to clang-format doc

Summary:
This commit adds a chapter 'CLion integration' to ClangFormat.rst. 
The official announcement of clang-format support in CLion 2019.1: https://blog.jetbrains.com/clion/2019/03/clion-2019-1-embedded-dev-clangformat-memory-view/

Patch by Marina Kalashina 

Reviewers: djasper, sylvestre.ledru, krasimir

Reviewed By: sylvestre.ledru

Subscribers: jdoerfert, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D60115

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@357566 91177308-0d34-0410-b5e6-96231b3b80d8

docs/ClangFormat.rst

@@ -165,6 +165,19 @@ menu item by renaming the script, and can assign the menu item a keyboard
 shortcut in the BBEdit preferences, under Menus & Shortcuts.
 
 
+CLion Integration
+==================
+
+:program:`clang-format` is integrated into `CLion <https://www.jetbrains
+.com/clion/>`_ as an alternative code formatter. It is disabled by default and
+can be turned on in Settings/Preferences | Editor | Code Style.
+
+If :program:`clang-format` support is enabled, CLion detects config files when
+opening a project and suggests overriding the current IDE settings. Code style
+rules from the ``.clang-format`` files are then applied automatically to all
+editor actions, including auto-completion, code generation, and refactorings.
+
+
 Visual Studio Integration
 =========================