document the existence of a global QlBuiltins module

Author: ginsbach

docs/codeql/ql-language-reference/name-resolution.rst

@@ -199,7 +199,7 @@ The namespaces containing all the built-in entities are called **global namespac
 and are automatically available in any module.
 In particular: 
 
-    - The **global module namespace** is empty.
+    - The **global module namespace** has a single entry ``QlBuiltins``.
     - The **global type namespace** has entries for the :ref:`primitive types <primitive-types>` ``int``, ``float``, 
       ``string``, ``boolean``, and ``date``, as well as any :ref:`database types <database-types>` defined in the database schema.
     - The **global predicate namespace** includes all the `built-in predicates <https://codeql.github.com/docs/ql-language-reference/ql-language-specification/#built-ins>`_,

docs/codeql/ql-language-reference/ql-language-specification.rst

@@ -120,7 +120,7 @@ A *definite* environment has at most one entry for each key. Resolution is uniqu
 Global environments
 ~~~~~~~~~~~~~~~~~~~
 
-The global module environment is empty.
+The global module environment has a single entry ``QlBuiltins``.
 
 The global type environment has entries for the primitive types ``int``, ``float``, ``string``, ``boolean``, and ``date``, as well as any types defined in the database schema.