Mention specializations in extension

Signed-off-by: Larsen, Steffen <[email protected]>

Author: steffenlarsen

sycl/doc/extensions/supported/sycl_ext_oneapi_bfloat16.asciidoc

@@ -303,6 +303,23 @@ int main(int argc, char *argv[]) {
 }
 ----
 
+=== Standard C++ library specializations
+
+The `bfloat16` class has specializations of the `std::numeric_limits` and
+`std::hash` standard C++ library classes. That is, an implementation must obey
+the following statements:
+
+ 1. A specialization of `std::hash` for `sycl::ext::oneapi::bfloat16` must exist
+    in the SYCL implementation that returns a unique value such that if two
+    instances of `sycl::ext::oneapi::bfloat16` are equal, in accordance with the
+    `==` operator, then their resulting hash values are also equal and
+    subsequently if two hash values are not equal, then their corresponding
+    instances are also not equal.
+ 2. A specialztion of `std::numeric_limits` for `sycl::ext::oneapi::bfloat16`
+    defining the arithmetic properties of the `sycl::ext::oneapi::bfloat16` in
+    accordance with the requirements specified by the standard C++ library
+    specification.
+
 == Revision History
 
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