Re-add 2x missing CMake IMPL_ flags to the Wiki (#585)

* Add ccmake recommendation

* Re-add Kokkos_ENABLE_IMPL_CUDA_MALLOC_ASYNC

* Re-add Kokkos_ENABLE_IMPL_HPX_ASYNC_DISPATCH

* Add warning about IMPL flags

* The --> Your

* Update docs/source/keywords.rst

Co-authored-by: Damien L-G <dalg24+github@gmail.com>

* Update docs/source/keywords.rst

Co-authored-by: Damien L-G <dalg24+github@gmail.com>

* Update docs/source/keywords.rst

Co-authored-by: Daniel Arndt <arndtd@ornl.gov>

* Update docs/source/keywords.rst

Co-authored-by: Daniel Arndt <arndtd@ornl.gov>

* Update docs/source/keywords.rst

Co-authored-by: Daniel Arndt <arndtd@ornl.gov>

* Elevate note on IMPL keywords to the top

* Change link to Wiki, not github PR

* Fix link

* Improve changes

* typo

---------

Co-authored-by: Damien L-G <dalg24+github@gmail.com>
Co-authored-by: Daniel Arndt <arndtd@ornl.gov>
Co-authored-by: Damien L-G <dalg24@gmail.com>

docs/source/keywords.rst

@@ -9,6 +9,15 @@ CMake Keywords
 
    Recall that to set a keyword in CMake you used the syntax ``-Dkeyword_name=value``.
 
+.. note::
+   The ``ccmake`` graphical user interface offers a convenient way to explore
+   available CMake options and their current values. It may be more up to date
+   with the Kokkos version that you are using.
+   **A word of warning:** variables with names containing ``IMPL`` are private
+   implementation details. Avoid modifying these unless you have a deep
+   understanding of their implications and are aware that they might change
+   without notice.
+
 
 This page is organized in four sections:
 
@@ -206,6 +215,13 @@ Backend-specific options
       * Use unified memory (UM) by default for CUDA
       * ``OFF``
 
+    * * ``Kokkos_ENABLE_IMPL_CUDA_MALLOC_ASYNC``
+      * Use ``cudaMallocAsync`` (requires CUDA Toolkit version 11.2 or higher). This
+	optimization may improve performance in applications with multiple CUDA streams per device, but it
+	is known to be incompatible with MPI distributions built on older versions of UCX
+	and many Cray MPICH instances. See `known issues <known-issues.html#cuda>`_.
+      * (see below)
+
     * * ``Kokkos_ENABLE_HIP_MULTIPLE_KERNEL_INSTANTIATIONS``
       * Instantiate multiple kernels at compile time - improve performance but increase compile time
       * ``OFF``
@@ -217,10 +233,18 @@ Backend-specific options
     * * ``Kokkos_ENABLE_ATOMICS_BYPASS``
       * Disable atomics when no host parallel nor device backend is enabled for Serial only builds (since Kokkos 4.3)
       * ``OFF``
-
+
+    * * ``Kokkos_ENABLE_IMPL_HPX_ASYNC_DISPATCH``
+      * Enable asynchronous dispatch for the HPX backend
+      * ``ON``
 
+
 ``Kokkos_ENABLE_CUDA_LAMBDA`` default value is ``OFF`` until 3.7 and ``ON`` since 4.0
 
+``Kokkos_ENABLE_IMPL_CUDA_MALLOC_ASYNC`` default value is ``OFF`` except in 4.2, 4.3, and 4.4
+
+
+
 Development
 -----------
 These are intended for developers of Kokkos.  If you are a user, you probably