title: Interpreting git diff output
body: <p>I been using git for years but never used diff command and I started to use it today but I really don't understand the output...  I had a file and I removed line 3 and 4 and I got the following output but can someone help me understand what the lines of the output means in dummy terms. thanks</p>
  
  <pre><code>$ git diff
  diff --git a/README.txt b/README.txt
  index 15827f4..8115e72 100644
  --- a/README.txt
  +++ b/README.txt
  @@ -1,4 +1,2 @@
   this file
   adding like
  -line 3
  -
  </code></pre>