Delete QL spec articles and add README

Author: Shati Patel

docs/language/ql-spec/index.rst

@@ -1,24 +1,5 @@
-QL specifications
-#################
+README
+######
 
-.. index:: specification
-
-
-For a formal specification of the QL language, including a description of syntax, terminology, and other technical details, please consult the QL language specification.
-
-For information on the terminology and syntax used in QLDoc comments, please consult the QLDoc comment specification.
-
-.. toctree::
-   :maxdepth: 2
-   
-   language
-
-   qldoc
-
-
-Search
-******
-
-.. * :ref:`genindex`
-
-* :ref:`search`
+The specifications have moved to ``ql/docs/language/ql-handbook``.
+See https://github.com/github/semmle-docs/issues/21 for details of the restructuring.