message: Add some doc for qlm
diff: @@ -546,6 +546,40 @@ For the `exatn-pmps` simulator, there are additional options that users can set
  If either `backend-json` or `backend` is provided, the `exatn-pmps` simulator will simulate the backend noise associated with each quantum gate.
  +Atos QLM
  +++++++++
  +
  +XACC provides an Accelerator interface to the Atos QLM simulator (plugin name: "atos-qlm") via the QLMaaS (QLM-as-a-service) API.
  +Users need to have a remote account (QLMaaS) to use this functionality.
  +
  +Note: ORNL users should contact Travis Humble to request a QLMaaS account for the ORNL's QLM machine.
  +
  +Prerequisites: ``myqlm`` and ``qlmaas`` Python packages on your local machine.
  +These packages can be installed via pip.
  +
  +Connection configuration set-up:
  +
  +- Method 1 (**recommended**):
  +create a file named `.qlm_config` at the `$HOME` directory with the following information.
  +Please note that the host address can be change to access other QLM machines if you have access to them.
  +
  +.. code::
  +
  + host: quantumbull.ornl.gov
  + username: <your QLM user name>
  + password: <your QLM password>
  +
  +- Method 2: provide the "username" and "password" fields when retrieving the qlm Accelerator, e.g.
  +
  +.. code:: cpp
  +
  + auto qlm = xacc::getAccelerator("atos-qlm", {{"username", "<your QLM user name>"}, {"password", "<your QLM password>"}});
  +
  +
  +- Method 3: reusing your QLMaaS configuration if you have one.
  +
  +For example, you have created the configuration using the Python `qlmaas` package, which is saved to `$HOME/.qlmaas/config.ini`. In this case, you don't need to provide any additional information. It should just work.
  +
  QuaC
  ++++
  The `QuaC <https://github.com/ORNL-QCI/QuaC/tree/xacc-integration>`_ accelerator is a pulse-level accelerator (simulation only) that can execute quantum circuits at both gate and pulse (analog) level.
  