title: the command `brew install watchman` runs `chmod` but fails to install eventually
body: <pre><code>brew install --HEAD watchman
  ==&gt; Cloning https://github.com/facebook/watchman.git
  Updating /Library/Caches/Homebrew/watchman--git
  ==&gt; Checking out branch master
  ==&gt; ./autogen.sh
  ==&gt; ./configure --prefix=/usr/local/Cellar/watchman/HEAD --with-pcre
  ==&gt; make
  ==&gt; make install
  install: chmod 777 /: Operation not permitted
  touch //.not-empty
  touch: //.not-empty: Permission denied
  make[1]: *** [install-exec-local] Error 1
  make: *** [install-am] Error 2
  couldn't understand kern.osversion `14.5.0'
  
  READ THIS: https://git.io/brew-troubleshooting
  </code></pre>
  
  <p>It is trying to <code>chmod 777 /</code> which is not good. Why is it trying to do that? Feels like that shouldn't be allowed. I tried to uninstall watchman and reinstall with this command to get a react-native to start working.</p>
  
  <p>Followed steps here: <a href="https://github.com/facebook/react-native/issues/239" rel="nofollow">https://github.com/facebook/react-native/issues/239</a></p>
  
  <p><a href="https://facebook.github.io/react-native/docs/troubleshooting.html" rel="nofollow">https://facebook.github.io/react-native/docs/troubleshooting.html</a></p>