Knob to enforce blank line between module docstring and modeline/shebang

This commit adds functionality to allow the placement of a newline
between the module's docstring, and the modeline/shebang if it exists.

Fixes #208.
diff --git a/README.rst b/README.rst
index 3b43d29..ccc74d9 100644
--- a/README.rst
+++ b/README.rst
@@ -322,6 +322,9 @@
             def method():
                 pass
 
+``BLANK_LINE_BEFORE_MODULE_DOCSTRING``
+    Insert a blank line before a module docstring.
+
 ``BLANK_LINE_BEFORE_CLASS_DOCSTRING``
     Insert a blank line before a class-level docstring.