bundle installation fails on MacBook Pro M1

[ekimike]

I wasn't able to execute successfully the command

bundle install from docs/README.md

The message I got was:

An error occurred while installing racc (1.6.0),

Then I installed XCode, and run the same command again: bundle install

So, not sure if there could be a warning on the README.md file for people who use Mac. If you consider adding that warning, I'd like to do it.

[manovotn]

I do not have Mac to verify this but if it's indeed the case, I see no harm in adding a small note into the doc.
Feel free to send a PR.