title: What is OPAM's shell hook?
body: <p>During initialization of OPAM I got this message:</p>
  
  <blockquote>
    <p>A hook can be added to opam's init scripts to ensure that the shell
    remains in sync with the opam environment when they are loaded. Set
    that up? [y/N]</p>
  </blockquote>
  
  <p>Could you clarify what does this mean?</p>
  
  <p>I've tried to find out it here: <a href="https://github.com/ocaml/opam/search?q=hook&amp;unscoped_q=hook" rel="nofollow noreferrer">https://github.com/ocaml/opam/search?q=hook&amp;unscoped_q=hook</a></p>
  
  <p>I heard this word before, but what is "shell hook"? What it is used for? Why it asks me to choose? :)</p>