title: gfortran command not found after installing with 'brew install gcc'
body: <p>I have Apple's Command Line Tools installed but that doesn't include <code>gfortran</code>. I have therefore installed gcc from homebrew (which includes <code>gfortran</code>)</p>
  
  <pre><code>brew install gcc
  </code></pre>
  
  <p>But then I get this warning</p>
  
  <pre><code>Warning: gcc-6.2.0 already installed, it's just not linked
  </code></pre>
  
  <p>So I try to link it</p>
  
  <pre><code>brew link gcc
  </code></pre>
  
  <p>with this result</p>
  
  <pre><code>Linking /usr/local/Cellar/gcc/6.2.0...
  Error: Could not symlink share/man/man7/fsf-funding-6.7
  /usr/local/share/man/man7 is not writable.
  </code></pre>
  
  <p>And here I'm stuck. I don't know how to resolve this error. How can I link <code>gcc</code>, or even better, why isn't it linked from the beginning?</p>