Add install instructions for clang version 10 to cpp11 webpage (#191)

Author: sbearrows

vignettes/internals.Rmd

@@ -56,9 +56,15 @@ covr::report(cpp11_coverage())
 
 ## Code formatting
 
-This project uses [clang-format](https://clang.llvm.org/docs/ClangFormat.html) to automatically format the c++ code.
+This project uses [clang-format](https://clang.llvm.org/docs/ClangFormat.html) (version 10) to automatically format the c++ code.
+
+You can run `make format` to re-format all code in the project. If your system does not have `clang-format` version 10, this can be installed using a [homebrew tap](https://github.com/r-lib/homebrew-taps) at the command line with `brew install r-lib/taps/clang-format@10`.
+
+You may need to link the newly installed version 10. To do so, run `brew unlink clang-format` followed by `brew link clang-format@10`.
+
+Alternatively many IDEs support automatically running `clang-format` every time files are written.
+
 
-You can run `make format` to re-format all code in the project. Alternatively many IDEs support automatically running `clang-format` every time files are written.
 
 ## Code organization