Added a caveat that you should add the Python scripts folder to your …

…path after installing with Homebrew. Closes #27.

howdoi.rb

@@ -9,4 +9,15 @@ def install
     setup_args = ['setup.py', 'install']
     system "python", *setup_args
   end
+
+  def scripts_folder
+    HOMEBREW_PREFIX/"share/python"
+  end
+
+  def caveats
+    <<-EOS.undent
+      To run the `howdoi` command, you'll need to add Python's script directory to your PATH:
+        #{scripts_folder}
+    EOS
+  end
 end