add a touch of text on the backends

Author: jmitrevs

docs/backend/oneapi.rst

@@ -2,11 +2,11 @@
 oneAPI
 ======
 
-The ``oneAPI`` backend of hls4ml is designed for deploying NNs on Intel/Altera FPGAs. It will eventually
-replace the ``Quartus`` backend, which targeted Intel HLS. (Quartus continues to be used with IP produced by the
-``oneAPI`` backend.) This section discusses details of the ``oneAPI`` backend.
+The **oneAPI** backend of hls4ml is designed for deploying NNs on Intel/Altera FPGAs. It will eventually
+replace the **Quartus** backend, which targeted Intel HLS. (Quartus continues to be used with IP produced by the
+**oneAPI** backend.) This section discusses details of the **oneAPI** backend.
 
-The ``oneAPI`` code uses SYCL kernels to implement the logic that is deployed on FPGAs. It naturally leads to the
+The **oneAPI** code uses SYCL kernels to implement the logic that is deployed on FPGAs. It naturally leads to the
 accelerator style of programming. In the SYCL HLS (IP Component) flow, which is currently the only flow supported, the
 kernel becomes the IP, and the "host code" becomes the testbench. An accelerator flow, with easier deployment on
 PCIe accelerator boards, is planned to be added in the future.
@@ -18,7 +18,7 @@ produces the library used for calling the ``predict`` function from hls4ml. The
 in hls4ml interact with the cmake system, so one does not need to manually use the build system, but it there
 if desired.
 
-The ``oneAPI`` backend, like the ``Quartus`` backend, only implements the ``Resource`` strategy for the layers. There
+The **oneAPI** backend, like the **Quartus** backend, only implements the ``Resource`` strategy for the layers. There
 is no ``Latency`` implementation of any of the layers.
 
 Note:  currently tracing and external weights (i.e. setting BramFactor) are not supported.

docs/backend/quartus.rst

@@ -3,6 +3,10 @@ Quartus
 =======
 
 .. warning::
-    Quartus backend is deprecated and will be removed in a future version. Users should migrate to oneAPI backend.
+    The **Quartus** backend is deprecated and will be removed in a future version. Users should migrate to the **oneAPI** backend.
 
-*TODO expand this section*
+The **Quartus** backend of hls4ml is designed for deploying NNs on Intel/Altera FPGAs. It uses the discontinued Intel HLS compiler. The **oneAPI** backend should be preferred for new projects.
+The **oneAPI** backend contains the migrated the HLS code from this backend, with significantly better io_stream support, though the **oneAPI** backend does not yet support profiling, tracing,
+or the BramFactor option supported by the **Quartus** backend.  Nevertheless, little or no further development is expected for this backend.
+
+The **Quartus** backend only implements the ``Resource`` strategy for the layers. There is no ``Latency`` implementation of any of the layers.

docs/backend/vitis.rst

@@ -2,6 +2,11 @@
 Vivado/Vitis
 ============
 
-``Vivado`` and ``Vitis`` backends are aimed for use with Xilinx FPGAs. They are currently the most advanced and well-supported backends of ``hls4ml``.
+The **Vivado** and **Vitis** backends are aimed for use with AMD/Xilinx FPGAs. The **Vivado** backend targets the discontinued ``Vivado HLS`` compiler, while
+the **Vitis** backend targets the ``Vitis HLS`` compiler. Both are designed to produce IP for incorporation in ``Vivado`` designs. (See :doc:`VivadoAccelerator <accelerator>`
+for generating easily-deployable models with ``Vivado HLS``.) The ``Vitis`` accelerator flow is not directly supported, though HLS produced with the **Vitis**
+backend can be easily incorporated into Vitis kernel.
+
+Users should generally use the **Vitis** backend for new designs that target AMD/Xilinx FPGAs; new ``hls4ml`` developments will not necessarily be backported to
+the **Vivado** backend.
 
-*TODO expand this section*