Recommend using git-clang-format in Contributing Guidelines

Author: gumb0

CONTRIBUTING.md

@@ -5,12 +5,13 @@
 
 2. **Code formatting** rules are described by the [Clang-Format Style Options] file [.clang-format].
    Please use the [clang-format] tool to format your code _changes_ accordingly.
-   
-   Example:
-   
-       clang-format -i -lines=146:159 libevm/JitVM.cpp
+   [git-clang-format] tool is useful to limit reformatting to your changes only:
+
+       git clang-format          # to reformat the changes in the working directory
+       git clang-format <commit> # to reformat commits between specified commit and HEAD
 
 
 [Clang-Format Style Options]: https://clang.llvm.org/docs/ClangFormatStyleOptions.html
 [clang-format]:               https://clang.llvm.org/docs/ClangFormat.html
 [.clang-format]:              .clang-format
+[git-clang-format]:           https://llvm.org/svn/llvm-project/cfe/trunk/tools/clang-format/git-clang-format