Added software section. Marshal is populated (mostly points to Marshal's own readthedocs). Spike is a stub.

docs/Software/FireMarshal.rst

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+FireMarshal
+=================
+
+FireMarshal is a workload generation tool for RISC-V based systems. It
+currently only supports the FireSim FPGA-accelerated simulation platform.
+
+**Workloads** in FireMarshal consist of a series of **Jobs** that are assigned
+to logical nodes in the target system. If no jobs are specified, then the
+workload is considered ``uniform`` and only a single image will be produced for
+all nodes in the system. Workloads are described by a json file and a
+corresponding workload directory and can inherit their definitions from
+existing workloads. Typically, workload configurations are kept in
+``workloads/`` although you can use any directory you like. We provide a few
+basic workloads to start with including buildroot or Fedora-based linux
+distributions and bare-metal.
+
+Once you define a workload, the ``marshal`` command will produce a
+corresponding boot-binary and rootfs for each job in the workload. This binary
+and rootfs can then be launched on qemu or spike (for functional simulation), or
+installed to a platform for running on real RTL (currently only FireSim is
+automated).
+
+To get started, checkout the full `FireMarshal documentation <https://firemarshal.readthedocs.io/en/latest/index.html>`_.