docs: quantity_point documentation fixed

docs/reference/core/concepts.rst

@@ -73,3 +73,8 @@ Concepts
       the elements of `ratio`), :expr:`T * T` and :expr:`T / T` must be valid,
     - otherwise, :expr:`T * std::int64_t`, :expr:`std::int64_t * T`, and :expr:`T / std::int64_t`
       must be valid.
+
+.. concept:: template<typename T> QuantityPoint
+
+    A concept matching all quantity points in the library. Satisfied by all instantiations of
+    :class:`quantity_point`.

docs/reference/core/types.rst

@@ -5,6 +5,7 @@ Types
     :maxdepth: 1
 
     types/quantity
+    types/quantity_point
     types/dimensions
     types/units
     types/prefixes

docs/reference/core/types/quantity_point.rst

@@ -0,0 +1,6 @@
+Quantity Point
+==============
+
+.. doxygenclass:: units::quantity_point
+   :members:
+   :undoc-members: