Added basic ctuple documentation.

docs/src/userguide/language_basics.rst

@@ -119,6 +119,9 @@ You can read more about them in :ref:`extension-types`.
 Types
 -----
 
+Types
+-----
+
 Cython uses the normal C syntax for C types, including pointers.  It provides
 all the standard C types, namely ``char``, ``short``, ``int``, ``long``,
 ``long long`` as well as their ``unsigned`` versions, e.g. ``unsigned int``.
@@ -148,6 +151,13 @@ typing and instead interpreted as C ``int``, ``long``, and ``float``
 respectively, as statically typing variables with these Python
 types has zero advantages.
 
+Cython provides an accelerated and typed equivalent of a Python tuple.
+A ``ctuple`` is assembled from any valid C types, for example::
+
+    cdef (double, int) bar
+
+They can be used like a Python tuple, including as function arguments and as return types.
+
 While these C types can be vastly faster, they have C semantics.
 Specifically, the integer types overflow
 and the C ``float`` type only has 32 bits of precision
@@ -208,6 +218,11 @@ using normal C declaration syntax. For example,::
     cdef int eggs(unsigned long l, float f):
         ...
 
+''ctuples'' may also be used::
+
+    cdef (int, float) chips((long, long, double) t):
+        ...
+
 When a parameter of a Python function is declared to have a C data type, it is
 passed in as a Python object and automatically converted to a C value, if
 possible. In other words, the definition of ``spam`` above is equivalent to