Add note about Clang version used

Author: kkaefer

README.md

@@ -1,6 +1,7 @@
 # XcodeClangFormat
 
 ### [⚙ Download Latest Release](https://github.com/mapbox/XcodeClangFormat/releases/latest)
+Uses `clang-format` from [Clang 10](https://releases.llvm.org/10.0.0/tools/clang/docs/ClangFormat.html)
 
 ...or install with Homebrew: `brew cask install xcodeclangformat`