Add the --no-color option to the git call in the doc when using clang-format-diff

llvm-svn: 288605
diff --git a/clang/tools/clang-format/clang-format-diff.py b/clang/tools/clang-format/clang-format-diff.py
index 5e728f5..ffa30e7 100755
--- a/clang/tools/clang-format/clang-format-diff.py
+++ b/clang/tools/clang-format/clang-format-diff.py
@@ -17,7 +17,7 @@
 lines. This is useful to reformat all the lines touched by a specific patch.
 Example usage for git/svn users:
 
-  git diff -U0 HEAD^ | clang-format-diff.py -p1 -i
+  git diff -U0 --no-color HEAD^ | clang-format-diff.py -p1 -i
   svn diff --diff-cmd=diff -x-U0 | clang-format-diff.py -i
 
 """